Spring Boot Features

This section dives into the details of Spring Boot. Here you can learn about the key features that you may want to use and customize. If you have not already done so, you might want to read the " getting-started.html " and " using-spring-boot.html " sections, so that you have a good grounding of the basics.

The SpringApplication class provides a convenient way to bootstrap a Spring application that is started from a main() method. In many situations, you can delegate to the static SpringApplication.run method, as shown in the following example:

public static void main(String[] args) {
    SpringApplication.run(MySpringConfiguration.class, args);
When your application starts, you should see something similar to the following output:
  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::   v2.2.0.M5
2013-07-31 00:08:16.117  INFO 56603 --- [           main] o.s.b.s.app.SampleApplication            : Starting SampleApplication v0.1.0 on mycomputer with PID 56603 (/apps/myapp.jar started by pwebb)
2013-07-31 00:08:16.166  INFO 56603 --- [           main] ationConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@6e5a8246: startup date [Wed Jul 31 00:08:16 PDT 2013]; root of context hierarchy
2014-03-04 13:09:54.912  INFO 41370 --- [           main] .t.TomcatServletWebServerFactory : Server initialized with port: 8080
2014-03-04 13:09:56.501  INFO 41370 --- [           main] o.s.b.s.app.SampleApplication            : Started SampleApplication in 2.992 seconds (JVM running for 3.658)
By default, INFO logging messages are shown, including some relevant startup details,
such as the user that launched the application. If you need a log level other than INFO,
you can set it, as described in Log Levels,
1.1. Startup Failure

If your application fails to start, registered FailureAnalyzers get a chance to provide
a dedicated error message and a concrete action to fix the problem. For instance, if you
start a web application on port 8080 and that port is already in use, you should see
something similar to the following message:
***************************
APPLICATION FAILED TO START
***************************
Description:
Embedded servlet container failed to start. Port 8080 was already in use.
Action:
Identify and stop the process that's listening on port 8080 or configure this application to listen on another port.
If no failure analyzers are able to handle the exception, you can still display the full
conditions report to better understand what went wrong. To do so, you need to
enable the debug property or
enable DEBUG logging for
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener.
For instance, if you are running your application by using java -jar, you can enable
the debug property as follows:
$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug
1.2. Lazy Initialization

SpringApplication allows an application to be initialized lazily. When lazy
initialization is enabled, beans are created as they are needed rather than during
application startup. As a result, enabling lazy initialization can reduce the time that
it takes your application to start. In a web application, enabling lazy initialization
will result in many web-related beans not being initialized until an HTTP request is
received.
A downside of lazy initialization is that it can delay the discovery of a problem with
the application. If a misconfigured bean is initialized lazily, a failure will no longer
occur during startup and the problem will only become apparent when the bean is
initialized. Care must also be taken to ensure that the JVM has sufficient memory to
accommodate all of the application’s beans and not just those that are initialized during
startup. For these reasons, lazy initialization is not enabled by default and it is
recommended that fine-tuning of the JVM’s heap size is done before enabling lazy
initialization.
Lazy initialization can be enabled programatically using the lazyInitialization method
on SpringApplicationBuilder or the setLazyInitialization method on
SpringApplication. Alternatively, it can be enabled using the
spring.main.lazy-initialization property as shown in the following example:
spring.main.lazy-initialization=true
If you want to disable lazy initialization for certain beans while using lazy
initialization for the rest of the application, you can explicitly set their lazy attribute
to false using the @Lazy(false) annotation.
1.3. Customizing the Banner

The banner that is printed on start up can be changed by adding a banner.txt file to
your classpath or by setting the spring.banner.location property to the location of such
a file. If the file has an encoding other than UTF-8, you can set spring.banner.charset.
In addition to a text file, you can also add a banner.gif, banner.jpg, or banner.png
image file to your classpath or set the spring.banner.image.location property. Images
are converted into an ASCII art representation and printed above any text banner.
Inside your banner.txt file, you can use any of the following placeholders:
Table 1. Banner variables
${application.version}
The version number of your application, as declared in MANIFEST.MF. For example,
Implementation-Version: 1.0 is printed as 1.0.
${application.formatted-version}
The version number of your application, as declared in MANIFEST.MF and formatted for
display (surrounded with brackets and prefixed with v). For example (v1.0).
${spring-boot.version}
The Spring Boot version that you are using. For example 2.2.0.M5.
${spring-boot.formatted-version}
The Spring Boot version that you are using, formatted for display (surrounded with
brackets and prefixed with v). For example (v2.2.0.M5).
${Ansi.NAME} (or ${AnsiColor.NAME}, ${AnsiBackground.NAME}, ${AnsiStyle.NAME})
Where NAME is the name of an ANSI escape code. See
AnsiPropertySource for details.
${application.title}
The title of your application, as declared in MANIFEST.MF. For example
Implementation-Title: MyApp is printed as MyApp.
The SpringApplication.setBanner(…) method can be used if you want to generate
a banner programmatically. Use the org.springframework.boot.Banner interface and
implement your own printBanner() method.
You can also use the spring.main.banner-mode property to determine if the banner has
to be printed on System.out (console), sent to the configured logger (log), or not
produced at all (off).
The printed banner is registered as a singleton bean under the following name:
springBootBanner.
1.4. Customizing SpringApplication

If the SpringApplication defaults are not to your taste, you can instead create a local
instance and customize it. For example, to turn off the banner, you could write:
public static void main(String[] args) {
    SpringApplication app = new SpringApplication(MySpringConfiguration.class);
    app.setBannerMode(Banner.Mode.OFF);
    app.run(args);
The constructor arguments passed to SpringApplication are configuration sources
for Spring beans. In most cases, these are references to @Configuration classes, but
they could also be references to XML configuration or to packages that should be scanned.
It is also possible to configure the SpringApplication by using an
application.properties file. See Externalized Configuration for details.

For a complete list of the configuration options, see the
SpringApplication Javadoc.
1.5. Fluent Builder API

If you need to build an ApplicationContext hierarchy (multiple contexts with a
parent/child relationship) or if you prefer using a “fluent” builder API, you can
use the SpringApplicationBuilder.




    

The SpringApplicationBuilder lets you chain together multiple method calls and includes
parent and child methods that let you create a hierarchy, as shown in the following
example:
new SpringApplicationBuilder()
        .sources(Parent.class)
        .child(Application.class)
        .bannerMode(Banner.Mode.OFF)
        .run(args);
There are some restrictions when creating an ApplicationContext hierarchy. For
example, Web components must be contained within the child context, and the same
Environment is used for both parent and child contexts. See the
SpringApplicationBuilder
Javadoc for full details.
1.6. Application Events and Listeners

In addition to the usual Spring Framework events, such as
ContextRefreshedEvent,
a SpringApplication sends some additional application events.
Some events are actually triggered before the ApplicationContext is created, so you
cannot register a listener on those as a @Bean. You can register them with the
SpringApplication.addListeners(…) method or the
SpringApplicationBuilder.listeners(…) method.
If you want those listeners to be registered automatically, regardless of the way the
application is created, you can add a META-INF/spring.factories file to your project
and reference your listener(s) by using the
org.springframework.context.ApplicationListener key, as shown in the following example:
org.springframework.context.ApplicationListener=com.example.project.MyListener
An ApplicationStartingEvent is sent at the start of a run but before any processing,
except for the registration of listeners and initializers.
An ApplicationEnvironmentPreparedEvent is sent when the Environment to be used in
the context is known but before the context is created.
An ApplicationContextInitializedEvent is sent when the ApplicationContext is prepared
and ApplicationContextInitializers have been called but before any bean definitions are loaded.
An ApplicationPreparedEvent is sent just before the refresh is started but after bean
definitions have been loaded.
An ApplicationStartedEvent is sent after the context has been refreshed but before any
application and command-line runners have been called.
An ApplicationReadyEvent is sent after any application and command-line runners have
been called. It indicates that the application is ready to service requests.
An ApplicationFailedEvent is sent if there is an exception on startup.
The above list only includes SpringApplicationEvent`s that are tied to a `SpringApplication.
In addition to these, the following events are also published after ApplicationPreparedEvent
and before ApplicationStartedEvent:
A WebServerInitializedEvent is sent after the WebServer is ready. ServletWebServerInitializedEvent
and ReactiveWebServerInitializedEvent are the servlet and reactive variants respectively.
Application events are sent by using Spring Framework’s event publishing mechanism. Part
of this mechanism ensures that an event published to the listeners in a child context is
also published to the listeners in any ancestor contexts. As a result of this, if your
application uses a hierarchy of SpringApplication instances, a listener may receive
multiple instances of the same type of application event.
To allow your listener to distinguish between an event for its context and an event for
a descendant context, it should request that its application context is injected and then
compare the injected context with the context of the event. The context can be injected
by implementing ApplicationContextAware or, if the listener is a bean, by using
@Autowired.
1.7. Web Environment

A SpringApplication attempts to create the right type of ApplicationContext on your
behalf. The algorithm used to determine a WebApplicationType is fairly simple:
If Spring MVC is not present and Spring WebFlux is present, an
AnnotationConfigReactiveWebServerApplicationContext is used
Otherwise, AnnotationConfigApplicationContext is used
This means that if you are using Spring MVC and the new WebClient from Spring WebFlux in
the same application, Spring MVC will be used by default. You can override that easily
by calling setWebApplicationType(WebApplicationType).
It is also possible to take complete control of the ApplicationContext type that is
used by calling setApplicationContextClass(…).
1.8. Accessing Application Arguments

If you need to access the application arguments that were passed to
SpringApplication.run(…), you can inject a
org.springframework.boot.ApplicationArguments bean. The ApplicationArguments
interface provides access to both the raw String[] arguments as well as parsed option
and non-option arguments, as shown in the following example:
import org.springframework.boot.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.stereotype.*;
@Component
public class MyBean {
    @Autowired
    public MyBean(ApplicationArguments args) {
        boolean debug = args.containsOption("debug");
        List<String> files = args.getNonOptionArgs();
        // if run with "--debug logfile.txt" debug=true, files=["logfile.txt"]
Spring Boot also registers a CommandLinePropertySource with the Spring
Environment. This lets you also inject single application arguments by using the
@Value annotation.
1.9. Using the ApplicationRunner or CommandLineRunner

If you need to run some specific code once the SpringApplication has started, you can
implement the ApplicationRunner or CommandLineRunner interfaces. Both interfaces work
in the same way and offer a single run method, which is called just before
SpringApplication.run(…) completes.
The CommandLineRunner interfaces provides access to application arguments as a simple
string array, whereas the ApplicationRunner uses the ApplicationArguments interface
discussed earlier. The following example shows a CommandLineRunner with a run method:
import org.springframework.boot.*;
import org.springframework.stereotype.*;
@Component
public class MyBean implements CommandLineRunner {
    public void run(String... args) {
        // Do something...
If several CommandLineRunner or ApplicationRunner beans are defined that must be
called in a specific order, you can additionally implement the
org.springframework.core.Ordered interface or use the
org.springframework.core.annotation.Order annotation.
1.10. Application Exit

Each SpringApplication registers a shutdown hook with the JVM to ensure that the
ApplicationContext closes gracefully on exit. All the standard Spring lifecycle
callbacks (such as the DisposableBean interface or the @PreDestroy annotation) can be
used.
In addition, beans may implement the org.springframework.boot.ExitCodeGenerator
interface if they wish to return a specific exit code when SpringApplication.exit() is
called. This exit code can then be passed to System.exit() to return it as a status
code, as shown in the following example:
@SpringBootApplication
public class ExitCodeApplication {
    @Bean
    public ExitCodeGenerator exitCodeGenerator() {
        return () -> 42;
    public static void main(String[] args) {
        System.exit(SpringApplication.exit(SpringApplication.run(ExitCodeApplication.class, args)));
Also, the ExitCodeGenerator interface may be implemented by exceptions. When such an
exception is encountered, Spring Boot returns the exit code provided by the implemented
getExitCode() method.
1.11. Admin Features

It is possible to enable admin-related features for the application by specifying the
spring.application.admin.enabled property. This exposes the
SpringApplicationAdminMXBean
on the platform MBeanServer. You could use this feature to administer your Spring Boot
application remotely. This feature could also be useful for any service wrapper
implementation.
Spring Boot lets you externalize your configuration so that you can work with the same
application code in different environments. You can use properties files, YAML files,
environment variables, and command-line arguments to externalize configuration. Property
values can be injected directly into your beans by using the @Value annotation,
accessed through Spring’s Environment abstraction, or be
bound to structured
objects through @ConfigurationProperties.
Spring Boot uses a very particular PropertySource order that is designed to allow
sensible overriding of values. Properties are considered in the following order:
Devtools global settings properties
on your home directory (~/.spring-boot-devtools.properties when devtools is active).
@TestPropertySource
annotations on your tests.
properties attribute on your tests. Available on
@SpringBootTest and the
annotations for testing a particular slice of your application.
Command line arguments.
Properties from SPRING_APPLICATION_JSON (inline JSON embedded in an environment
variable or system property).
ServletConfig init parameters.
ServletContext init parameters.
JNDI attributes from java:comp/env.
Java System properties (System.getProperties()).
OS environment variables.
A RandomValuePropertySource that has properties only in random.*.
Profile-specific
application properties outside of your packaged jar
(application-{profile}.properties and YAML variants).
Profile-specific
application properties packaged inside your jar (application-{profile}.properties
and YAML variants).
Application properties outside of your packaged jar (application.properties and YAML
variants).
Application properties packaged inside your jar (application.properties and YAML
variants).
@PropertySource
annotations on your @Configuration classes.
Default properties (specified by setting SpringApplication.setDefaultProperties).
import org.springframework.stereotype.*;
import org.springframework.beans.factory.annotation.*;
@Component
public class MyBean {
    @Value("${name}")
    private String name;
    // ...
On your application classpath (for example, inside your jar) you can have an
application.properties file that provides a sensible default property value for name.
When running in a new environment, an application.properties file can be provided
outside of your jar that overrides the name. For one-off testing, you can launch with a
specific command line switch (for example, java -jar app.jar --name="Spring").
The SPRING_APPLICATION_JSON properties can be supplied on the command line with an
environment variable. For example, you could use the following line in a UN*X
shell:
$ SPRING_APPLICATION_JSON='{"acme":{"name":"test"}}' java -jar myapp.jar
In the preceding example, you end up with acme.name=test in the Spring Environment.
You can also supply the JSON as spring.application.json in a System property, as shown
in the following example:
$ java -Dspring.application.json='{"name":"test"}' -jar myapp.jar
You can also supply the JSON by using a command line argument, as shown in the following
example:
$ java -jar myapp.jar --spring.application.json='{"name":"test"}'
You can also supply the JSON as a JNDI variable, as follows:
java:comp/env/spring.application.json.
2.1. Configuring Random Values

The RandomValuePropertySource is useful for injecting random values (for example, into
secrets or test cases). It can produce integers, longs, uuids, or strings, as shown in the
following example:
my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number.less.than.ten=${random.int(10)}
my.number.in.range=${random.int[1024,65536]}
The random.int* syntax is OPEN value (,max) CLOSE where the OPEN,CLOSE are any
character and value,max are integers. If max is provided, then value is the minimum
value and max is the maximum value (exclusive).
2.2. Accessing Command Line Properties

By default, SpringApplication converts any command line option arguments (that is,
arguments starting with --, such as --server.port=9000) to a property and adds
them to the Spring Environment. As mentioned previously, command line properties always
take precedence over other property sources.
If you do not want command line properties to be added to the Environment, you can
disable them by using SpringApplication.setAddCommandLineProperties(false).
2.3. Application Property Files

SpringApplication loads properties from application.properties files in the following
locations and adds them to the Spring Environment:
If you do not like application.properties as the configuration file name, you can
switch to another file name by specifying a spring.config.name environment property.
You can also refer to an explicit location by using the spring.config.location
environment property (which is a comma-separated list of directory locations or file
paths). The following example shows how to specify a different file name:




    

$ java -jar myproject.jar --spring.config.name=myproject
The following example shows how to specify two locations:
$ java -jar myproject.jar --spring.config.location=classpath:/default.properties,classpath:/override.properties
spring.config.name and spring.config.location are used very early to
determine which files have to be loaded, so they must be defined as an environment
property (typically an OS environment variable, a system property, or a command-line
argument).
If spring.config.location contains directories (as opposed to files), they should end
in / (and, at runtime, be appended with the names generated from spring.config.name
before being loaded, including profile-specific file names). Files specified in
spring.config.location are used as-is, with no support for profile-specific variants,
and are overridden by any profile-specific properties.
Config locations are searched in reverse order. By default, the configured locations are
classpath:/,classpath:/config/,file:./,file:./config/. The resulting search order is
the following:
When custom config locations are configured by using spring.config.location, they
replace the default locations. For example, if spring.config.location is configured with
the value classpath:/custom-config/,file:./custom-config/, the search order becomes the
following:
Alternatively, when custom config locations are configured by using
spring.config.additional-location, they are used in addition to the default locations.
Additional locations are searched before the default locations. For example, if
additional locations of classpath:/custom-config/,file:./custom-config/ are configured,
the search order becomes the following:
This search ordering lets you specify default values in one configuration file and then
selectively override those values in another. You can provide default values for your
application in application.properties (or whatever other basename you choose with
spring.config.name) in one of the default locations. These default values can then be
overridden at runtime with a different file located in one of the custom locations.
If you use environment variables rather than system properties, most operating
systems disallow period-separated key names, but you can use underscores instead (for
example, SPRING_CONFIG_NAME instead of spring.config.name).
If your application runs in a container, then JNDI properties (in java:comp/env)
or servlet context initialization parameters can be used instead of, or as well as,
environment variables or system properties.
2.4. Profile-specific Properties

In addition to application.properties files, profile-specific properties can also be
defined by using the following naming convention: application-{profile}.properties. The
Environment has a set of default profiles (by default, [default]) that are used if no
active profiles are set. In other words, if no profiles are explicitly activated, then
properties from application-default.properties are loaded.
Profile-specific properties are loaded from the same locations as standard
application.properties, with profile-specific files always overriding the non-specific
ones, whether or not the profile-specific files are inside or outside your
packaged jar.
If several profiles are specified, a last-wins strategy applies. For example, profiles
specified by the spring.profiles.active property are added after those configured
through the SpringApplication API and therefore take precedence.
If you have specified any files in spring.config.location, profile-specific
variants of those files are not considered. Use directories in
spring.config.location if you want to also use profile-specific properties.
2.5. Placeholders in Properties

The values in application.properties are filtered through the existing Environment
when they are used, so you can refer back to previously defined values (for example, from
System properties).
app.name=MyApp
app.description=${app.name} is a Spring Boot application
You can also use this technique to create “short” variants of existing Spring Boot
properties. See the howto.html how-to for
details.
2.6. Encrypting Properties

Spring Boot does not provide any built in support for encrypting property values, however,
it does provide the hook points necessary to modify values contained in the Spring
Environment. The EnvironmentPostProcessor interface allows you to manipulate the
Environment before the application starts. See [howto-customize-the-environment-or-application-context]
for details.
If you’re looking for a secure way to store credentials and passwords, the
Spring Cloud Vault project provides
support for storing externalized configuration in
HashiCorp Vault.
2.7. Using YAML Instead of Properties

YAML is a superset of JSON and, as such, is a convenient format for
specifying hierarchical configuration data. The SpringApplication class automatically
supports YAML as an alternative to properties whenever you have the
SnakeYAML library on your classpath.
2.7.1. Loading YAML

Spring Framework provides two convenient classes that can be used to load YAML documents.
The YamlPropertiesFactoryBean loads YAML as Properties and the YamlMapFactoryBean
loads YAML as a Map.
For example, consider the following YAML document:
environments:
        url: https://dev.example.com
        name: Developer Setup
    prod:
        url: https://another.example.com
        name: My Cool App
The preceding example would be transformed into the following properties:
environments.dev.url=https://dev.example.com
environments.dev.name=Developer Setup
environments.prod.url=https://another.example.com
environments.prod.name=My Cool App
YAML lists are represented as property keys with [index] dereferencers. For example,
consider the following YAML:
   servers:
       - dev.example.com
       - another.example.com

The preceding example would be transformed into these properties:
my.servers[0]=dev.example.com
my.servers[1]=another.example.com
To bind to properties like that by using Spring Boot’s Binder utilities (which is what
@ConfigurationProperties does), you need to have a property in the target bean of type
java.util.List (or Set) and you either need to provide a setter or initialize it with
a mutable value. For example, the following example binds to the properties shown
previously:
@ConfigurationProperties(prefix="my")
public class Config {
    private List<String> servers = new ArrayList<String>();
    public List<String> getServers() {
        return this.servers;
2.7.2. Exposing YAML as Properties in the Spring Environment

The YamlPropertySourceLoader class can be used to expose YAML as a PropertySource in
the Spring Environment. Doing so lets you use the @Value annotation with placeholders
syntax to access YAML properties.
2.7.3. Multi-profile YAML Documents

You can specify multiple profile-specific YAML documents in a single file by using a
spring.profiles key to indicate when the document applies, as shown in the following
example:
server:
    address: 192.168.1.100
spring:
    profiles: development
server:
    address: 127.0.0.1
spring:
    profiles: production & eu-central
server:
    address: 192.168.1.120
In the preceding example, if the development profile is active, the server.address
property is 127.0.0.1. Similarly, if the production and eu-central profiles are
active, the server.address property is 192.168.1.120. If the development,
production and eu-central profiles are not enabled, then the value for the property
is 192.168.1.100.
spring.profiles can therefore contain a simple profile name (for example production)
or a profile expression. A profile expression allows for more complicated profile logic
to be expressed, for example production & (eu-central | eu-west). Check the
reference guide for more
details.
If none are explicitly active when the application context starts, the default profiles
are activated. So, in the following YAML, we set a value for spring.security.user.password
that is available only in the "default" profile:
server:
  port: 8000
spring:
  profiles: default
  security:
    user:
      password: weak
Whereas, in the following example, the password is always set because it is not attached
to any profile, and it would have to be explicitly reset in all other profiles as
necessary:
server:
  port: 8000
spring:
  security:
    user:
      password: weak
Spring profiles designated by using the spring.profiles element may optionally be
negated by using the ! character. If both negated and non-negated profiles are
specified for a single document, at least one non-negated profile must match, and no
negated profiles may match.
2.7.4. YAML Shortcomings

YAML files cannot be loaded by using the @PropertySource annotation. So, in the case
that you need to load values that way, you need to use a properties file.
Using the multi YAML document syntax in profile-specific YAML files can lead to unexpected
behavior. For example, consider the following config in a file called application-dev.yml,
with the dev profile being active:
server:
  port: 8000
spring:
  profiles: !test
  security:
    user:
      password: weak
In the example above, profile negation and profile expressions will not behave as expected.
We recommend that you don’t combine profile-specific YAML files and multiple YAML documents and stick
to using only one of them.
2.8. Type-safe Configuration Properties

Using the @Value("${property}") annotation to inject configuration properties can
sometimes be cumbersome, especially if you are working with multiple properties or your
data is hierarchical in nature. Spring Boot provides an alternative method of working
with properties that lets strongly typed beans govern and validate the configuration of
your application.
2.8.1. JavaBean properties binding

It is possible to bind a bean declaring standard JavaBean properties as shown in the
following example:
package com.example;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.springframework.boot.context.properties.ConfigurationProperties;
@ConfigurationProperties("acme")
public class AcmeProperties {
    private boolean enabled;
    private InetAddress remoteAddress;
    private final Security security = new Security();
    public boolean isEnabled() { ... }
    public void setEnabled(boolean enabled) { ... }
    public InetAddress getRemoteAddress() { ... }
    public void setRemoteAddress(InetAddress remoteAddress) { ... }
    public Security getSecurity() { ... }
    public static class Security {
        private String username;
        private String password;
        private List<String> roles = new ArrayList<>(Collections.singleton("USER"));
        public String getUsername() { ... }
        public void setUsername(String username) { ... }
        public String getPassword() { ... }
        public void setPassword(String password) { ... }
        public List<String> getRoles() { ... }
        public void setRoles(List<String> roles) { ... }
The preceding POJO defines the following properties:
acme.security.username, with a nested "security" object whose name is determined by
the name of the property. In particular, the return type is not used at all there and
could have been SecurityProperties.
acme.security.password.
acme.security.roles, with a collection of String that defaults to USER.
Such arrangement relies on a default empty constructor and getters and setters are usually
mandatory, since binding is through standard Java Beans property descriptors, just like in
Spring MVC. A setter may be omitted in the following cases:
Maps, as long as they are initialized, need a getter but not necessarily a setter,
since they can be mutated by the binder.
Collections and arrays can be accessed either through an index (typically with YAML) or
by using a single comma-separated value (properties). In the latter case, a setter is
mandatory. We recommend to always add a setter for such types. If you initialize a
collection, make sure it is not immutable (as in the preceding example).
If nested POJO properties are initialized (like the Security field in the preceding
example), a setter is not required. If you want the binder to create the instance on the
fly by using its default constructor, you need a setter.
Some people use Project Lombok to add getters and setters automatically. Make sure that
Lombok does not generate any particular constructor for such a type, as it is used
automatically by the container to instantiate the object.
Finally, only standard Java Bean properties are considered and binding on static
properties is not supported.




    

2.8.2. Constructor binding

The example in the previous section can be rewritten in an immutable fashion as shown in
the following example:
package com.example;
import java.net.InetAddress;
import java.util.List;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.context.properties.DefaultValue;
@ConfigurationProperties("acme")
public class AcmeProperties {
    private final boolean enabled;
    private final InetAddress remoteAddress;
    private final Security security;
    public AcmeProperties(boolean enabled, InetAddress remoteAddress, Security security) {
        this.enabled = enabled;
        this.remoteAddress = remoteAddress;
        this.security = security;
    public boolean isEnabled() { ... }
    public InetAddress getRemoteAddress() { ... }
    public Security getSecurity() { ... }
    public static class Security {
        private final String username;
        private final String password;
        private final List<String> roles;
        public Security(String username, String password,
                @DefaultValue("USER") List<String> roles) {
            this.username = username;
            this.password = password;
            this.roles = roles;
        public String getUsername() { ... }
        public String getPassword() { ... }
        public List<String> getRoles() { ... }
In this setup one, and only one constructor must be defined with the list of properties
that you wish to bind and not other properties than the ones in the constructor are bound.
Default values can be specified using @DefaultValue and the same conversion service will
be applied to coerce the String value to the target type of a missing property.
2.8.3. Enabling @ConfigurationProperties-annotated types

Spring Boot provides an infrastructure to bind such types and register them as beans
automatically. If your application uses @SpringBootApplication, classes annotated with
@ConfigurationProperties will automatically be scanned and registered as beans. By default,
scanning will occur from the package of the class that declares this annotation. If you want
to define specific packages to scan, you can do so using an explicit @ConfigurationPropertiesScan
directive on your @SpringBootApplication-annotated class as shown in the following example:
@SpringBootApplication
@ConfigurationPropertiesScan({ "com.example.app", "org.acme.another" })
public class MyApplication {
Sometimes, classes annotated with @ConfigurationProperties might not be suitable
for scanning, for example, if you’re developing your own auto-configuration. In these
cases, you can specify the list of types to process on any @Configuration class as
shown in the following example:
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(AcmeProperties.class)
public class MyConfiguration {
When the @ConfigurationProperties bean is registered using scanning or via
@EnableConfigurationProperties, the bean has a conventional name: <prefix>-<fqn>,
where <prefix> is the environment key prefix specified in the @ConfigurationProperties
annotation and <fqn> is the fully qualified name of the bean. If the annotation does not
provide any prefix, only the fully qualified name of the bean is used.
The bean name in the example above is acme-com.example.AcmeProperties.
We recommend that @ConfigurationProperties only deal with the environment and, in
particular, does not inject other beans from the context. In particular, it is not
possible to inject other beans using the constructor as this would trigger the constructor
binder that only deals with the environment.
For corner cases, setter injection can be used or any of the *Aware interfaces provided
by the framework (such as EnvironmentAware if you need access to the Environment).
Annotating a @ConfigurationProperties type with @Component will result in two
beans of the same type if the type is also scanned as part of classpath scanning. If you want
to register the bean yourself using @Component, consider disabling scanning of
@ConfigurationProperties.
2.8.4. Using @ConfigurationProperties-annotated types

This style of configuration works particularly well with the SpringApplication external
YAML configuration, as shown in the following example:
# application.yml
acme:
    remote-address: 192.168.1.1
    security:
        username: admin
        roles:
          - USER
          - ADMIN
# additional configuration as required
To work with @ConfigurationProperties beans, you can inject them in the same way
as any other bean, as shown in the following example:
@Service
public class MyService {
    private final AcmeProperties properties;
    @Autowired
    public MyService(AcmeProperties properties) {
        this.properties = properties;
    //...
    @PostConstruct
    public void openConnection() {
        Server server = new Server(this.properties.getRemoteAddress());
        // ...
Using @ConfigurationProperties also lets you generate metadata files that can be
used by IDEs to offer auto-completion for your own keys. See the
appendix for details.
2.8.5. Third-party Configuration

As well as using @ConfigurationProperties to annotate a class, you can also use it on
public @Bean methods. Doing so can be particularly useful when you want to bind
properties to third-party components that are outside of your control.
To configure a bean from the Environment properties, add @ConfigurationProperties to
its bean registration, as shown in the following example:
@ConfigurationProperties(prefix = "another")
@Bean
public AnotherComponent anotherComponent() {
Any JavaBean property defined with the another prefix is mapped onto that
AnotherComponent bean in manner similar to the preceding AcmeProperties example.
2.8.6. Relaxed Binding

Spring Boot uses some relaxed rules for binding Environment properties to
@ConfigurationProperties beans, so there does not need to be an exact match between the
Environment property name and the bean property name.  Common examples where this is
useful include dash-separated environment properties (for example, context-path binds
to contextPath), and capitalized environment properties (for example, PORT binds to
port).
For example, consider the following @ConfigurationProperties class:
@ConfigurationProperties(prefix="acme.my-project.person")
public class OwnerProperties {
    private String firstName;
    public String getFirstName() {
        return this.firstName;
    public void setFirstName(String firstName) {
        this.firstName = firstName;
In the preceding example, the following properties names can all be used:
Table 2. relaxed binding
acme.my-project.person.first-name
Kebab case, which is recommended for use in .properties and .yml files.
acme.myProject.person.firstName
Standard camel case syntax.
acme.my_project.person.first_name
Underscore notation, which is an alternative format for use in .properties and .yml
files.
ACME_MYPROJECT_PERSON_FIRSTNAME
Upper case format, which is recommended when using system environment variables.
Properties Files
Camel case, kebab case, or underscore notation
Standard list syntax using [ ] or comma-separated values
YAML Files
Camel case, kebab case, or underscore notation
Standard YAML list syntax or comma-separated values
Environment Variables
Upper case format with underscore as the delimiter. _ should not be used within a
property name
Numeric values surrounded by underscores, such as MY_ACME_1_OTHER = my.acme[1].other
System properties
Camel case, kebab case, or underscore notation
Standard list syntax using [ ] or comma-separated values
When binding to Map properties, if the key contains anything other than lowercase
alpha-numeric characters or -, you need to use the bracket notation so that the original
value is preserved. If the key is not surrounded by [], any characters that are not alpha-numeric
or - are removed. For example, consider binding the following properties to a Map:
acme:
    "[/key1]": value1
    "[/key2]": value2
    /key3: value3
The properties above will bind to a Map with /key1, /key2 and key3 as the keys in the map.
2.8.7. Merging Complex Types

When lists are configured in more than one place, overriding works by replacing the entire
list.
For example, assume a MyPojo object with name and description attributes that are
null by default. The following example exposes a list of MyPojo objects from
AcmeProperties:
@ConfigurationProperties("acme")
public class AcmeProperties {
    private final List<MyPojo> list = new ArrayList<>();
    public List<MyPojo> getList() {
        return this.list;
Consider the following configuration:
acme:
  list:
    - name: my name
      description: my description
spring:
  profiles: dev
acme:
  list:
    - name: my another name
If the dev profile is not active, AcmeProperties.list contains one MyPojo entry,
as previously defined. If the dev profile is enabled, however, the list still
contains only one entry (with a name of my another name and a description of null).
This configuration does not add a second MyPojo instance to the list, and it does not
merge the items.
When a List is specified in multiple profiles, the one with the highest priority
(and only that one) is used. Consider the following example:
acme:
  list:
    - name: my name
      description: my description
    - name: another name
      description: another description
spring:
  profiles: dev
acme:
  list:
    - name: my another name
In the preceding example, if the dev profile is active, AcmeProperties.list contains
one MyPojo entry (with a name of my another name and a description of null).
For YAML, both comma-separated lists and YAML lists can be used for
completely overriding the contents of the list.
For Map properties, you can bind with property values drawn from multiple sources. However,
for the same property in multiple sources, the one with the highest priority is used.
The following example exposes a Map<String, MyPojo> from AcmeProperties:
@ConfigurationProperties("acme")
public class AcmeProperties {
    private final Map<String, MyPojo> map = new HashMap<>();
    public Map<String, MyPojo> getMap() {
        return this.map;
Consider the following configuration:
acme:
    key1:
      name: my name 1
      description: my description 1
spring:
  profiles: dev
acme:
    key1:
      name: dev name 1
    key2:
      name: dev name 2
      description: dev description 2
If the dev profile is not active, AcmeProperties.map contains one entry with key key1
(with a name of my name 1 and a description of my description 1).
If the dev profile is enabled, however, map contains two entries with keys key1
(with a name of dev name 1 and a description of my description 1) and
key2 (with a name of dev name 2 and a description of dev description 2).
2.8.8. Properties Conversion

Spring Boot attempts to coerce the external application properties to the right type when
it binds to the @ConfigurationProperties beans. If you need custom type conversion, you
can provide a ConversionService bean (with a bean named conversionService) or custom
property editors (through a CustomEditorConfigurer bean) or custom Converters (with
bean definitions annotated as @ConfigurationPropertiesBinding).
As this bean is requested very early during the application lifecycle, make sure to
limit the dependencies that your ConversionService is using. Typically, any dependency
that you require may not be fully initialized at creation time. You may want to rename
your custom ConversionService if it is not required for configuration keys coercion and
only rely on custom converters qualified with @ConfigurationPropertiesBinding.
Converting durations

Spring Boot has dedicated support for expressing durations. If you expose a
java.time.Duration property, the following formats in application properties are
available:
A regular long representation (using milliseconds as the default unit unless a
@DurationUnit has been specified)
The standard ISO-8601 format
used by
java.time.Duration




    

A more readable format where the value and the unit are coupled (e.g. 10s means 10
seconds)
    @DurationUnit(ChronoUnit.SECONDS)
    private Duration sessionTimeout = Duration.ofSeconds(30);
    private Duration readTimeout = Duration.ofMillis(1000);
    public Duration getSessionTimeout() {
        return this.sessionTimeout;
    public void setSessionTimeout(Duration sessionTimeout) {
        this.sessionTimeout = sessionTimeout;
    public Duration getReadTimeout() {
        return this.readTimeout;
    public void setReadTimeout(Duration readTimeout) {
        this.readTimeout = readTimeout;
To specify a session timeout of 30 seconds, 30, PT30S and 30s are all equivalent. A
read timeout of 500ms can be specified in any of the following form: 500, PT0.5S and
500ms.
You can also use any of the supported units. These are:
The default unit is milliseconds and can be overridden using @DurationUnit as illustrated
in the sample above.
If you are upgrading from a previous version that is simply using Long to express
the duration, make sure to define the unit (using @DurationUnit) if it isn’t
milliseconds alongside the switch to Duration. Doing so gives a transparent upgrade path
while supporting a much richer format.
Converting Data Sizes

Spring Framework has a DataSize value type that allows to express size in bytes. If you
expose a DataSize property, the following formats in application properties are
available:
A regular long representation (using bytes as the default unit unless a
@DataSizeUnit has been specified)
A more readable format where the value and the unit are coupled (e.g. 10MB means 10
megabytes)
    private DataSize bufferSize = DataSize.ofMegabytes(2);
    private DataSize sizeThreshold = DataSize.ofBytes(512);
    public DataSize getBufferSize() {
        return this.bufferSize;
    public void setBufferSize(DataSize bufferSize) {
        this.bufferSize = bufferSize;
    public DataSize getSizeThreshold() {
        return this.sizeThreshold;
    public void setSizeThreshold(DataSize sizeThreshold) {
        this.sizeThreshold = sizeThreshold;
To specify a buffer size of 10 megabytes, 10 and 10MB are equivalent. A size threshold
of 256 bytes can be specified as 256 or 256B.
You can also use any of the supported units. These are:
If you are upgrading from a previous version that is simply using Long to express
the size, make sure to define the unit (using @DataSizeUnit) if it isn’t bytes alongside
the switch to DataSize. Doing so gives a transparent upgrade path while supporting a
much richer format.
2.8.9. @ConfigurationProperties Validation

Spring Boot attempts to validate @ConfigurationProperties classes whenever they are
annotated with Spring’s @Validated annotation. You can use JSR-303 javax.validation
constraint annotations directly on your configuration class. To do so, ensure that a
compliant JSR-303 implementation is on your classpath and then add constraint annotations
to your fields, as shown in the following example:
@ConfigurationProperties(prefix="acme")
@Validated
public class AcmeProperties {
    @NotNull
    private InetAddress remoteAddress;
    // ... getters and setters
Although nested properties will also be validated when bound, it’s good practice to
also annotate the associated field as @Valid. This ensure that validation is triggered
even if no nested properties are found. The following example builds on the preceding
AcmeProperties example:
@ConfigurationProperties(prefix="acme")
@Validated
public class AcmeProperties {
    @NotNull
    private InetAddress remoteAddress;
    @Valid
    private final Security security = new Security();
    // ... getters and setters
    public static class Security {
        @NotEmpty
        public String username;
        // ... getters and setters
You can also add a custom Spring Validator by creating a bean definition called
configurationPropertiesValidator. The @Bean method should be declared static. The
configuration properties validator is created very early in the application’s lifecycle,
and declaring the @Bean method as static lets the bean be created without having to
instantiate the @Configuration class. Doing so avoids any problems that may be caused
by early instantiation.
The spring-boot-actuator module includes an endpoint that exposes all
@ConfigurationProperties beans. Point your web browser to
/actuator/configprops or use the equivalent JMX endpoint. See the
"Production ready features"
section for details.
2.8.10. @ConfigurationProperties vs. @Value

The @Value annotation is a core container feature, and it does not provide the same
features as type-safe configuration properties. The following table summarizes the
features that are supported by @ConfigurationProperties and @Value:
If you define a set of configuration keys for your own components, we recommend you
group them in a POJO annotated with @ConfigurationProperties. You should also be aware
that, since @Value does not support relaxed binding, it is not a good candidate if you
need to provide the value by using environment variables.
Finally, while you can write a SpEL expression in @Value, such expressions are not
processed from application
property files.
Spring Profiles provide a way to segregate parts of your application configuration and
make it be available only in certain environments.  Any @Component, @Configuration
or @ConfigurationProperties can be marked with @Profile to limit when it is loaded,
as shown in the following example:
@Configuration(proxyBeanMethods = false)
@Profile("production")
public class ProductionConfiguration {
    // ...
If @ConfigurationProperties beans are registered via @EnableConfigurationProperties
instead of automatic scanning, the @Profile annotation needs to be specified on the @Configuration
class that has the @EnableConfigurationProperties annotation. In the case where @ConfigurationProperties
are scanned, @Profile can be specified on the @ConfigurationProperties class itself.
You can use a spring.profiles.active Environment property to specify which profiles
are active. You can specify the property in any of the ways described earlier in this
chapter. For example, you could include it in your application.properties, as shown in
the following example:
spring.profiles.active=dev,hsqldb
You could also specify it on the command line by using the following switch:
--spring.profiles.active=dev,hsqldb.
3.1. Adding Active Profiles

The spring.profiles.active property follows the same ordering rules as other
properties: The highest PropertySource wins. This means that you can specify active
profiles in application.properties and then replace them by using the command line
switch.
Sometimes, it is useful to have profile-specific properties that add to the active
profiles rather than replace them. The spring.profiles.include property can be used to
unconditionally add active profiles. The SpringApplication entry point also has a Java
API for setting additional profiles (that is, on top of those activated by the
spring.profiles.active property). See the setAdditionalProfiles() method in
SpringApplication.
For example, when an application with the following properties is run by using the
switch, --spring.profiles.active=prod, the proddb and prodmq profiles are also
activated:
my.property: fromyamlfile
spring.profiles: prod
spring.profiles.include:
  - proddb
  - prodmq
Remember that the spring.profiles property can be defined in a YAML document to
determine when this particular document is included in the configuration. See
[howto-change-configuration-depending-on-the-environment] for more details.
3.2. Programmatically Setting Profiles

You can programmatically set active profiles by calling
SpringApplication.setAdditionalProfiles(…) before your application runs. It is also
possible to activate profiles by using Spring’s ConfigurableEnvironment interface.
3.3. Profile-specific Configuration Files

Profile-specific variants of both application.properties (or application.yml) and
files referenced through @ConfigurationProperties are considered as files and loaded.
See "Profile-specific Properties" for details.
Spring Boot uses Commons Logging for all internal
logging but leaves the underlying log implementation open. Default configurations are
provided for
Java Util
Logging, Log4J2, and
Logback. In each case, loggers are pre-configured to use console
output with optional file output also available.
By default, if you use the “Starters”, Logback is used for logging. Appropriate Logback
routing is also included to ensure that dependent libraries that use Java Util Logging,
Commons Logging, Log4J, or SLF4J all work correctly.
There are a lot of logging frameworks available for Java. Do not worry if the above
list seems confusing. Generally, you do not need to change your logging dependencies and
the Spring Boot defaults work just fine.
2014-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2014-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: 'dispatcherServlet' to [/]
2014-03-05 10:57:51.702  INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
The following items are output:
4.2. Console Output

The default log configuration echoes messages to the console as they are written. By
default, ERROR-level, WARN-level, and INFO-level messages are logged. You can also
enable a “debug” mode by starting your application with a --debug flag.
$ java -jar myapp.jar --debug
When the debug mode is enabled, a selection of core loggers (embedded container,
Hibernate, and Spring Boot) are configured to output more information. Enabling the debug
mode does not configure your application to log all messages with DEBUG level.
Alternatively, you can enable a “trace” mode by starting your application with a
--trace flag (or trace=true in your application.properties). Doing so enables trace
logging for a selection of core loggers (embedded container, Hibernate schema generation,
and the whole Spring portfolio).
4.2.1. Color-coded Output

If your terminal supports ANSI, color output is used to aid readability. You can set
spring.output.ansi.enabled to a
supported value to override the auto
detection.
Color coding is configured by using the %clr conversion word. In its simplest form, the
converter colors the output according to the log level, as shown in the following
example:
%clr(%5p)
The following table describes the mapping of log levels to colors:
Alternatively, you can specify the color or style that should be used by providing it as
an option to the conversion. For example, to make the text yellow, use the following
setting:
%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}
The following colors and styles are supported:
4.3. File Output

By default, Spring Boot logs only to the console and does not write log files. If you
want to write log files in addition to the console output, you need to set a
logging.file.name or logging.file.path property (for example, in your
application.properties).
The following table shows how the logging.* properties can be used together:
Table 4. Logging properties
(none)
my.log
Writes to the specified log file. Names can be an exact location or relative to the
current directory.
(none)
Specific directory
/var/log
Writes spring.log to the specified directory. Names can be an exact location or
relative to the current directory.
Log files rotate when they reach 10 MB and, as with console output, ERROR-level,
WARN-level, and INFO-level messages are logged by default. Size limits can be changed
using the logging.file.max-size property. Previously rotated files are archived
indefinitely unless the logging.file.max-history property has been set. The total size
of log archives can be capped using logging.file.total-size-cap. When the total size of
log archives exceeds that threshold, backups will be deleted. To force log archive cleanup
on application startup, use the logging.file.clean-history-on-start property.
The logging system is initialized early in the application lifecycle. Consequently,
logging properties are not found in property files loaded through @PropertySource
annotations.
Logging properties are independent of the actual logging infrastructure. As a
result, specific configuration keys (such as logback.configurationFile for Logback) are
not managed by spring Boot.
4.4. Log Levels

All the supported logging systems can have the logger levels set in the Spring
Environment (for example, in application.properties) by using
logging.level.<logger-name>=<level> where level is one of TRACE, DEBUG, INFO, WARN,
ERROR, FATAL, or OFF. The root logger can be configured by using logging.level.root.




    

The following example shows potential logging settings in application.properties:
logging.level.root=WARN
logging.level.org.springframework.web=DEBUG
logging.level.org.hibernate=ERROR
4.5. Log Groups

It’s often useful to be able to group related loggers together so that they can all be
configured at the same time. For example, you might commonly change the logging levels for
all Tomcat related loggers, but you can’t easily remember top level packages.
To help with this, Spring Boot allows you to define logging groups in your Spring
Environment. For example, here’s how you could define a “tomcat” group by adding
it to your application.properties:
logging.group.tomcat=org.apache.catalina, org.apache.coyote, org.apache.tomcat
Once defined, you can change the level for all the loggers in the group with a single
line:
logging.level.tomcat=TRACE
Spring Boot includes the following pre-defined logging groups that can be used
out-of-the-box:
4.6. Custom Log Configuration

The various logging systems can be activated by including the appropriate libraries on
the classpath and can be further customized by providing a suitable configuration file in
the root of the classpath or in a location specified by the following Spring Environment
property: logging.config.
You can force Spring Boot to use a particular logging system by using the
org.springframework.boot.logging.LoggingSystem system property. The value should be the
fully qualified class name of a LoggingSystem implementation. You can also disable
Spring Boot’s logging configuration entirely by using a value of none.
Since logging is initialized before the ApplicationContext is created, it is
not possible to control logging from @PropertySources in Spring @Configuration files.
The only way to change the logging system or disable it entirely is via System properties.
When possible, we recommend that you use the -spring variants for your logging
configuration (for example, logback-spring.xml rather than logback.xml). If you use
standard configuration locations, Spring cannot completely control log initialization.
There are known classloading issues with Java Util Logging that cause problems
when running from an 'executable jar'. We recommend that you avoid it when running from
an 'executable jar' if at all possible.
logging.exception-conversion-word
LOG_EXCEPTION_CONVERSION_WORD
The conversion word used when logging exceptions.
logging.file.clean-history-on-start
LOG_FILE_CLEAN_HISTORY_ON_START
Whether to clean the archive log files on startup (if LOG_FILE enabled). (Only supported
with the default Logback setup.)
logging.file.name
LOG_FILE
If defined, it is used in the default log configuration.
logging.file.max-size
LOG_FILE_MAX_SIZE
Maximum log file size (if LOG_FILE enabled). (Only supported with the default Logback
setup.)
logging.file.max-history
LOG_FILE_MAX_HISTORY
Maximum number of archive log files to keep (if LOG_FILE enabled). (Only supported with
the default Logback setup.)
logging.file.path
LOG_PATH
If defined, it is used in the default log configuration.
logging.file.total-size-cap
LOG_FILE_TOTAL_SIZE_CAP
Total size of log backups to be kept (if LOG_FILE enabled). (Only supported with the
default Logback setup.)
logging.pattern.console
CONSOLE_LOG_PATTERN
The log pattern to use on the console (stdout). (Only supported with the default Logback
setup.)
logging.pattern.dateformat
LOG_DATEFORMAT_PATTERN
Appender pattern for log date format. (Only supported with the default Logback setup.)
logging.pattern.file
FILE_LOG_PATTERN
The log pattern to use in a file (if LOG_FILE is enabled). (Only supported with the
default Logback setup.)
logging.pattern.level
LOG_LEVEL_PATTERN
The format to use when rendering the log level (default %5p). (Only supported with the
default Logback setup.)
The current process ID (discovered if possible and when not already defined as an OS
environment variable).
If you want to use a placeholder in a logging property, you should use
Spring Boot’s syntax and not
the syntax of the underlying framework. Notably, if you use Logback, you should use :
as the delimiter between a property name and its default value and not use :-.
You can add MDC and other ad-hoc content to log lines by overriding only the
LOG_LEVEL_PATTERN (or logging.pattern.level with Logback). For example, if you use
logging.pattern.level=user:%X{user} %5p, then the default log format contains an MDC
entry for "user", if it exists, as shown in the following example.
2015-09-30 12:30:04.031 user:someone INFO 22174 --- [  nio-8080-exec-0] demo.Controller
Handling authenticated request
4.7. Logback Extensions

Spring Boot includes a number of extensions to Logback that can help with advanced
configuration. You can use these extensions in your logback-spring.xml configuration
file.
Because the standard logback.xml configuration file is loaded too early, you
cannot use extensions in it. You need to either use logback-spring.xml or define a
logging.config property.
The extensions cannot be used with Logback’s
configuration scanning. If you
attempt to do so, making changes to the configuration file results in an error similar to
one of the following being logged:
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]]
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]
4.7.1. Profile-specific Configuration

The <springProfile> tag lets you optionally include or exclude sections of
configuration based on the active Spring profiles. Profile sections are supported
anywhere within the <configuration> element. Use the name attribute to specify which
profile accepts the configuration. The <springProfile> tag can contain a simple profile
name (for example staging) or a profile expression. A profile expression allows for more
complicated profile logic to be expressed, for example
production & (eu-central | eu-west). Check the
reference guide for more
details. The following listing shows three sample profiles:
<springProfile name="staging">
    <!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>
<springProfile name="dev | staging">
    <!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>
<springProfile name="!production">
    <!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>
4.7.2. Environment Properties

The <springProperty> tag lets you expose properties from the Spring Environment for
use within Logback. Doing so can be useful if you want to access values from your
application.properties file in your Logback configuration. The tag works in a similar
way to Logback’s standard <property> tag. However, rather than specifying a direct
value, you specify the source of the property (from the Environment). If you need
to store the property somewhere other than in local scope, you can use the scope
attribute. If you need a fallback value (in case the property is not set in the
Environment), you can use the defaultValue attribute. The following example shows how
to expose properties for use within Logback:
<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
        defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
    <remoteHost>${fluentHost}</remoteHost>
</appender>
Spring Boot supports localized messages so that your application can cater to users
of different language preferences. By default, Spring Boot looks for the presence of
a messages resource bundle at the root of the classpath.
The auto-configuration applies when the default properties file for the configured
resource bundle is available (i.e. messages.properties by default). If your resource
bundle contains only language-specific properties files, you are required to add the
default. If no properties file is found that matches any of the configured base names,
there will be no auto-configured MessageSource.
The basename of the resource bundle as well as several other attributes can be configured
using the spring.messages namespace, as shown in the following example:
spring.messages.basename=messages,config.i18n.messages
spring.messages.fallback-to-system-locale=false
Auto-configuration for Jackson is provided and Jackson is part of
spring-boot-starter-json. When Jackson is on the classpath an ObjectMapper
bean is automatically configured. Several configuration properties are provided for
customizing the configuration of the
ObjectMapper.
6.2. Gson

Auto-configuration for Gson is provided. When Gson is on the classpath a Gson bean is
automatically configured.  Several spring.gson.* configuration properties are
provided for customizing the configuration. To take more control, one or more
GsonBuilderCustomizer beans can be used.
6.3. JSON-B

Auto-configuration for JSON-B is provided. When the JSON-B API and an implementation are
on the classpath a Jsonb bean will be automatically configured. The preferred JSON-B
implementation is Apache Johnzon for which dependency management is provided.
Spring Boot is well suited for web application development. You can create a
self-contained HTTP server by using embedded Tomcat, Jetty, Undertow, or Netty. Most web
applications use the spring-boot-starter-web module to get up and running quickly. You
can also choose to build reactive web applications by using the
spring-boot-starter-webflux module.
If you have not yet developed a Spring Boot web application, you can follow the
"Hello World!" example in the
Getting started section.

7.1. The “Spring Web MVC Framework”

The Spring Web MVC framework (often referred to as simply
“Spring MVC”) is a rich “model view controller” web framework. Spring MVC lets you
create special @Controller or @RestController beans to handle incoming HTTP requests.
Methods in your controller are mapped to HTTP by using @RequestMapping annotations.
The following code shows a typical @RestController that serves JSON data:
@RestController
@RequestMapping(value="/users")
public class MyRestController {
    @RequestMapping(value="/\{user}", method=RequestMethod.GET)
    public User getUser(@PathVariable Long user) {
        // ...
    @RequestMapping(value="/\{user}/customers", method=RequestMethod.GET)
    List<Customer> getUserCustomers(@PathVariable Long user) {
        // ...
    @RequestMapping(value="/\{user}", method=RequestMethod.DELETE)
    public User deleteUser(@PathVariable Long user) {
        // ...
Spring MVC is part of the core Spring Framework, and detailed information is available in
the  reference documentation. There are also several
guides that cover Spring MVC available at spring.io/guides.
7.1.1. Spring MVC Auto-configuration

Spring Boot provides auto-configuration for Spring MVC that works well with most
applications.
The auto-configuration adds the following features on top of Spring’s defaults:
Support for serving static resources, including support for WebJars (covered
later in this document)).
Automatic registration of Converter, GenericConverter, and Formatter beans.
Support for HttpMessageConverters (covered
later in this document).
Automatic registration of MessageCodesResolver (covered
later in this document).
Static index.html support.
Custom Favicon support (covered later in this
document).
Automatic use of a ConfigurableWebBindingInitializer bean (covered
later in this document).
If you want to keep Spring Boot MVC features and you want to add additional
MVC configuration (interceptors, formatters, view
controllers, and other features), you can add your own @Configuration class of type
WebMvcConfigurer but without @EnableWebMvc. If you wish to provide custom
instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or
ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter
instance to provide such components.
If you want to take complete control of Spring MVC, you can add your own @Configuration
annotated with @EnableWebMvc.




    

7.1.2. HttpMessageConverters

Spring MVC uses the HttpMessageConverter interface to convert HTTP requests and
responses. Sensible defaults are included out of the box. For example, objects can be
automatically converted to JSON (by using the Jackson library) or XML (by using the
Jackson XML extension, if available, or by using JAXB if the Jackson XML extension is not
available). By default, strings are encoded in UTF-8.
If you need to add or customize converters, you can use Spring Boot’s
HttpMessageConverters class, as shown in the following listing:
import org.springframework.boot.autoconfigure.http.HttpMessageConverters;
import org.springframework.context.annotation.*;
import org.springframework.http.converter.*;
@Configuration(proxyBeanMethods = false)
public class MyConfiguration {
    @Bean
    public HttpMessageConverters customConverters() {
        HttpMessageConverter<?> additional = ...
        HttpMessageConverter<?> another = ...
        return new HttpMessageConverters(additional, another);
Any HttpMessageConverter bean that is present in the context is added to the list of
converters. You can also override default converters in the same way.
7.1.3. Custom JSON Serializers and Deserializers

If you use Jackson to serialize and deserialize JSON data, you might want to write your
own JsonSerializer and JsonDeserializer classes. Custom serializers are usually
registered with Jackson through
a module, but Spring Boot provides an alternative @JsonComponent annotation that makes
it easier to directly register Spring Beans.
You can use the @JsonComponent annotation directly on JsonSerializer,
JsonDeserializer or KeyDeserializer implementations. You can also use it on classes
that contain serializers/deserializers as inner classes, as shown in the following example:
import java.io.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import org.springframework.boot.jackson.*;
@JsonComponent
public class Example {
    public static class Serializer extends JsonSerializer<SomeObject> {
        // ...
    public static class Deserializer extends JsonDeserializer<SomeObject> {
        // ...
All @JsonComponent beans in the ApplicationContext are automatically registered with
Jackson. Because @JsonComponent is meta-annotated with @Component, the usual
component-scanning rules apply.
Spring Boot also provides
JsonObjectSerializer and
JsonObjectDeserializer base
classes that provide useful alternatives to the standard Jackson versions when
serializing objects. See
JsonObjectSerializer
and JsonObjectDeserializer in
the Javadoc for details.
7.1.4. MessageCodesResolver

Spring MVC has a strategy for generating error codes for rendering error messages from
binding errors: MessageCodesResolver. If you set the
spring.mvc.message-codes-resolver.format property PREFIX_ERROR_CODE or
POSTFIX_ERROR_CODE, Spring Boot creates one for you (see the enumeration in
DefaultMessageCodesResolver.Format).
7.1.5. Static Content

By default, Spring Boot serves static content from a directory called /static (or
/public or /resources or /META-INF/resources) in the classpath or from the root of
the ServletContext.  It uses the ResourceHttpRequestHandler from Spring MVC so that
you can modify that behavior by adding your own WebMvcConfigurer and overriding the
addResourceHandlers method.
In a stand-alone web application, the default servlet from the container is also enabled
and acts as a fallback, serving content from the root of the ServletContext if Spring
decides not to handle it. Most of the time, this does not happen (unless you modify the
default MVC configuration), because Spring can always handle requests through the
DispatcherServlet.
By default, resources are mapped on /**, but you can tune that with the
spring.mvc.static-path-pattern property. For instance, relocating all resources to
/resources/** can be achieved as follows:
spring.mvc.static-path-pattern=/resources/**
You can also customize the static resource locations by using the
spring.resources.static-locations property (replacing the default values with a list of
directory locations). The root Servlet context path, "/", is automatically added as a
location as well.
In addition to the “standard” static resource locations mentioned earlier, a special
case is made for Webjars content. Any resources with a path in
/webjars/** are served from jar files if they are packaged in the Webjars format.
Do not use the src/main/webapp directory if your application is packaged as a jar.
Although this directory is a common standard, it works only with war packaging, and it
is silently ignored by most build tools if you generate a jar.
Spring Boot also supports the advanced resource handling features provided by Spring MVC,
allowing use cases such as cache-busting static resources or using version agnostic URLs
for Webjars.
To use version agnostic URLs for Webjars, add the webjars-locator-core dependency.
Then declare your Webjar. Using jQuery as an example, adding
"/webjars/jquery/jquery.min.js" results in
"/webjars/jquery/x.y.z/jquery.min.js". where x.y.z is the Webjar version.
If you use JBoss, you need to declare the webjars-locator-jboss-vfs
dependency instead of the webjars-locator-core. Otherwise, all Webjars resolve as a
404.
To use cache busting, the following configuration configures a cache busting solution for
all static resources, effectively adding a content hash, such as
<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>, in URLs:
spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**
Links to resources are rewritten in templates at runtime, thanks to a
ResourceUrlEncodingFilter that is auto-configured for Thymeleaf and FreeMarker. You
should manually declare this filter when using JSPs. Other template engines are currently
not automatically supported but can be with custom template macros/helpers and the use of
ResourceUrlProvider.
When loading resources dynamically with, for example, a JavaScript module loader,
renaming files is not an option. That is why other strategies are also supported and can
be combined. A "fixed" strategy adds a static version string in the URL without changing
the file name, as shown in the following example:
spring.resources.chain.strategy.content.enabled=true
spring.resources.chain.strategy.content.paths=/**
spring.resources.chain.strategy.fixed.enabled=true
spring.resources.chain.strategy.fixed.paths=/js/lib/
spring.resources.chain.strategy.fixed.version=v12
With this configuration, JavaScript modules located under "/js/lib/" use a fixed
versioning strategy ("/v12/js/lib/mymodule.js"), while other resources still use the
content one (<link href="/css/spring-2a2d595e6ed9a0b24f027f2b63b134d6.css"/>).
See ResourceProperties
for more supported options.
This feature has been thoroughly described in a dedicated
post and in Spring Framework’s
reference documentation.
7.1.6. Welcome Page

Spring Boot supports both static and templated welcome pages. It first looks for an
index.html file in the configured static content locations. If one is not found, it
then looks for an index template. If either is found, it is automatically used as the
welcome page of the application.
7.1.7. Custom Favicon

Spring Boot looks for a favicon.ico in the configured static content locations and the
root of the classpath (in that order). If such a file is present, it is automatically
used as the favicon of the application.
7.1.8. Path Matching and Content Negotiation

Spring MVC can map incoming HTTP requests to handlers by looking at the request path and
matching it to the mappings defined in your application (for example, @GetMapping
annotations on Controller methods).
Spring Boot chooses to disable suffix pattern matching by default, which means that
requests like "GET /projects/spring-boot.json" won’t be matched to
@GetMapping("/projects/spring-boot") mappings.
This is considered as a
best practice
for Spring MVC applications. This feature was mainly useful in the past for HTTP
clients which did not send proper "Accept" request headers; we needed to make sure
to send the correct Content Type to the client. Nowadays, Content Negotiation
is much more reliable.
There are other ways to deal with HTTP clients that don’t consistently send proper
"Accept" request headers. Instead of using suffix matching, we can use a query
parameter to ensure that requests like "GET /projects/spring-boot?format=json"
will be mapped to @GetMapping("/projects/spring-boot"):
spring.mvc.contentnegotiation.favor-parameter=true
# We can change the parameter name, which is "format" by default:
# spring.mvc.contentnegotiation.parameter-name=myparam
# We can also register additional file extensions/media types with:
spring.mvc.contentnegotiation.media-types.markdown=text/markdown
If you understand the caveats and would still like your application to use
suffix pattern matching, the following configuration is required:
spring.mvc.contentnegotiation.favor-path-extension=true
spring.mvc.pathmatch.use-suffix-pattern=true
Alternatively, rather than open all suffix patterns, it’s more secure to just support
registered suffix patterns:
spring.mvc.contentnegotiation.favor-path-extension=true
spring.mvc.pathmatch.use-registered-suffix-pattern=true
# You can also register additional file extensions/media types with:
# spring.mvc.contentnegotiation.media-types.adoc=text/asciidoc
7.1.9. ConfigurableWebBindingInitializer

Spring MVC uses a WebBindingInitializer to initialize a WebDataBinder for a
particular request. If you create your own ConfigurableWebBindingInitializer @Bean,
Spring Boot automatically configures Spring MVC to use it.
7.1.10. Template Engines

As well as REST web services, you can also use Spring MVC to serve dynamic HTML content.
Spring MVC supports a variety of templating technologies, including Thymeleaf,
FreeMarker, and JSPs. Also, many other templating engines include their own Spring MVC
integrations.
Spring Boot includes auto-configuration support for the following templating engines:
If possible, JSPs should be avoided. There are several
known limitations when using them with embedded
servlet containers.
Depending on how you run your application, IntelliJ IDEA orders the classpath
differently. Running your application in the IDE from its main method results in a
different ordering than when you run your application by using Maven or Gradle or from
its packaged jar. This can cause Spring Boot to fail to find the templates on the
classpath. If you have this problem, you can reorder the classpath in the IDE to place
the module’s classes and resources first. Alternatively, you can configure the template
prefix to search every templates directory on the classpath, as follows:
classpath*:/templates/.
7.1.11. Error Handling

By default, Spring Boot provides an /error mapping that handles all errors in a
sensible way, and it is registered as a “global” error page in the servlet container.
For machine clients, it produces a JSON response with details of the error, the HTTP
status, and the exception message. For browser clients, there is a “whitelabel” error
view that renders the same data in HTML format (to customize it, add a View that
resolves to error). To replace the default behavior completely, you can implement
ErrorController and register a bean definition of that type or add a bean of type
ErrorAttributes to use the existing mechanism but replace the contents.
The BasicErrorController can be used as a base class for a custom
ErrorController. This is particularly useful if you want to add a handler for a new
content type (the default is to handle text/html specifically and provide a fallback
for everything else). To do so, extend BasicErrorController, add a public method with a
@RequestMapping that has a produces attribute, and create a bean of your new type.
You can also define a class annotated with @ControllerAdvice to customize the JSON
document to return for a particular controller and/or exception type, as shown in the
following example:
@ControllerAdvice(basePackageClasses = AcmeController.class)
public class AcmeControllerAdvice extends ResponseEntityExceptionHandler {
    @ExceptionHandler(YourException.class)
    @ResponseBody
    ResponseEntity<?> handleControllerException(HttpServletRequest request, Throwable ex) {
        HttpStatus status = getStatus(request);
        return new ResponseEntity<>(new CustomErrorType(status.value(), ex.getMessage()), status);
    private HttpStatus getStatus(HttpServletRequest request) {
        Integer statusCode = (Integer) request.getAttribute("javax.servlet.error.status_code");
        if (statusCode == null) {
            return HttpStatus.INTERNAL_SERVER_ERROR;
        return HttpStatus.valueOf(statusCode);
In the preceding example, if YourException is thrown by a controller defined in the
same package as AcmeController, a JSON representation of the CustomErrorType POJO is
used instead of the ErrorAttributes representation.




    

Custom Error Pages

If you want to display a custom HTML error page for a given status code, you can add a
file to an /error folder. Error pages can either be static HTML (that is, added under
any of the static resource folders) or be built by using templates. The name of the file
should be the exact status code or a series mask.
For example, to map 404 to a static HTML file, your folder structure would be as
follows:
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors by using a FreeMarker template, your folder structure would be as
follows:
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.ftlh
             +- <other templates>

For more complex mappings, you can also add beans that implement the ErrorViewResolver
interface, as shown in the following example:
public class MyErrorViewResolver implements ErrorViewResolver {
    @Override
    public ModelAndView resolveErrorView(HttpServletRequest request,
            HttpStatus status, Map<String, Object> model) {
        // Use the request or status to optionally return a ModelAndView
        return ...
You can also use regular Spring MVC features such as
@ExceptionHandler methods and
@ControllerAdvice. The
ErrorController then picks up any unhandled exceptions.
Mapping Error Pages outside of Spring MVC

For applications that do not use Spring MVC, you can use the ErrorPageRegistrar
interface to directly register ErrorPages. This abstraction works directly with the
underlying embedded servlet container and works even if you do not have a Spring MVC
DispatcherServlet.
@Bean
public ErrorPageRegistrar errorPageRegistrar(){
    return new MyErrorPageRegistrar();
// ...
private static class MyErrorPageRegistrar implements ErrorPageRegistrar {
    @Override
    public void registerErrorPages(ErrorPageRegistry registry) {
        registry.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
If you register an ErrorPage with a path that ends up being handled by a Filter
(as is common with some non-Spring web frameworks, like Jersey and Wicket), then the
Filter has to be explicitly registered as an ERROR dispatcher, as shown in the
following example:
@Bean
public FilterRegistrationBean myFilter() {
    FilterRegistrationBean registration = new FilterRegistrationBean();
    registration.setFilter(new MyFilter());
    registration.setDispatcherTypes(EnumSet.allOf(DispatcherType.class));
    return registration;
Note that the default FilterRegistrationBean does not include the ERROR dispatcher
type.
CAUTION:When deployed to a servlet container, Spring Boot uses its error page filter to
forward a request with an error status to the appropriate error page. The request can only
be forwarded to the correct error page if the response has not already been committed. By
default, WebSphere Application Server 8.0 and later commits the response upon successful
completion of a servlet’s service method. You should disable this behavior by setting
com.ibm.ws.webcontainer.invokeFlushAfterService to false.
7.1.12. Spring HATEOAS

If you develop a RESTful API that makes use of hypermedia, Spring Boot provides
auto-configuration for Spring HATEOAS that works well with most applications. The
auto-configuration replaces the need to use @EnableHypermediaSupport and registers a
number of beans to ease building hypermedia-based applications, including a
LinkDiscoverers (for client side support) and an ObjectMapper configured to correctly
marshal responses into the desired representation. The ObjectMapper is customized by
setting the various spring.jackson.* properties or, if one exists, by a
Jackson2ObjectMapperBuilder bean.
You can take control of Spring HATEOAS’s configuration by using
@EnableHypermediaSupport. Note that doing so disables the ObjectMapper customization
described earlier.
7.1.13. CORS Support

Cross-origin resource sharing
(CORS) is a W3C specification implemented by
most browsers that lets you specify in a flexible
way what kind of cross-domain requests are authorized, instead of using some less secure
and less powerful approaches such as IFRAME or JSONP.
As of version 4.2, Spring MVC supports CORS.
Using controller method
CORS configuration with
@CrossOrigin
annotations in your Spring Boot application does not require any specific configuration.
Global CORS configuration can be
defined by registering a WebMvcConfigurer bean with a customized
addCorsMappings(CorsRegistry) method, as shown in the following example:
@Configuration(proxyBeanMethods = false)
public class MyConfiguration {
    @Bean
    public WebMvcConfigurer corsConfigurer() {
        return new WebMvcConfigurer() {
            @Override
            public void addCorsMappings(CorsRegistry registry) {
                registry.addMapping("/api/**");
7.2. The “Spring WebFlux Framework”

Spring WebFlux is the new reactive web framework introduced in Spring Framework 5.0.
Unlike Spring MVC, it does not require the Servlet API, is fully asynchronous and
non-blocking, and implements the Reactive Streams
specification through the Reactor project.
Spring WebFlux comes in two flavors: functional and annotation-based. The
annotation-based one is quite close to the Spring MVC model, as shown in the
following example:
@RestController
@RequestMapping("/users")
public class MyRestController {
    @GetMapping("/\{user}")
    public Mono<User> getUser(@PathVariable Long user) {
        // ...
    @GetMapping("/\{user}/customers")
    public Flux<Customer> getUserCustomers(@PathVariable Long user) {
        // ...
    @DeleteMapping("/\{user}")
    public Mono<User> deleteUser(@PathVariable Long user) {
        // ...
“WebFlux.fn”, the functional variant, separates the routing configuration from the
actual handling of the requests, as shown in the following example:
@Configuration(proxyBeanMethods = false)
public class RoutingConfiguration {
    @Bean
    public RouterFunction<ServerResponse> monoRouterFunction(UserHandler userHandler) {
        return route(GET("/\{user}").and(accept(APPLICATION_JSON)), userHandler::getUser)
                .andRoute(GET("/\{user}/customers").and(accept(APPLICATION_JSON)), userHandler::getUserCustomers)
                .andRoute(DELETE("/\{user}").and(accept(APPLICATION_JSON)), userHandler::deleteUser);
@Component
public class UserHandler {
    public Mono<ServerResponse> getUser(ServerRequest request) {
        // ...
    public Mono<ServerResponse> getUserCustomers(ServerRequest request) {
        // ...
    public Mono<ServerResponse> deleteUser(ServerRequest request) {
        // ...
WebFlux is part of the Spring Framework and detailed information is available in its
reference documentation.
Adding both spring-boot-starter-web and spring-boot-starter-webflux modules in
your application results in Spring Boot auto-configuring Spring MVC, not WebFlux. This
behavior has been chosen because many Spring developers add spring-boot-starter-webflux
to their Spring MVC application to use the reactive WebClient. You can still enforce
your choice by setting the chosen application type to
SpringApplication.setWebApplicationType(WebApplicationType.REACTIVE).
7.2.1. Spring WebFlux Auto-configuration

Spring Boot provides auto-configuration for Spring WebFlux that works well with most
applications.
The auto-configuration adds the following features on top of Spring’s defaults:
Configuring codecs for HttpMessageReader and HttpMessageWriter instances (described
later in this document).
Support for serving static resources, including support for WebJars (described
later in this document).
If you want to keep Spring Boot WebFlux features and you want to add additional
WebFlux configuration, you can add your own
@Configuration class of type WebFluxConfigurer but without @EnableWebFlux.
If you want to take complete control of Spring WebFlux, you can add your own
@Configuration annotated with @EnableWebFlux.
7.2.2. HTTP Codecs with HttpMessageReaders and HttpMessageWriters

Spring WebFlux uses the HttpMessageReader and HttpMessageWriter interfaces to convert
HTTP requests and responses. They are configured with CodecConfigurer to have sensible
defaults by looking at the libraries available in your classpath.
Spring Boot applies further customization by using CodecCustomizer instances. For
example, spring.jackson.* configuration keys are applied to the Jackson codec.
If you need to add or customize codecs, you can create a custom CodecCustomizer
component, as shown in the following example:
import org.springframework.boot.web.codec.CodecCustomizer;
@Configuration(proxyBeanMethods = false)
public class MyConfiguration {
    @Bean
    public CodecCustomizer myCodecCustomizer() {
        return codecConfigurer -> {
            // ...
You can also leverage Boot’s custom JSON serializers and
deserializers.
7.2.3. Static Content

By default, Spring Boot serves static content from a directory called /static (or
/public or /resources or /META-INF/resources) in the classpath. It uses the
ResourceWebHandler from Spring WebFlux so that you can modify that behavior by adding
your own WebFluxConfigurer and overriding the addResourceHandlers method.
By default, resources are mapped on /**, but you can tune that by setting the
spring.webflux.static-path-pattern property. For instance, relocating all resources to
/resources/** can be achieved as follows:
spring.webflux.static-path-pattern=/resources/**
You can also customize the static resource locations by using
spring.resources.static-locations. Doing so replaces the default values with a list of
directory locations. If you do so, the default welcome page detection switches to your
custom locations. So, if there is an index.html in any of your locations on startup, it
is the home page of the application.
In addition to the “standard” static resource locations listed earlier, a special case
is made for Webjars content. Any resources with a path in
/webjars/** are served from jar files if they are packaged in the Webjars format.
7.2.4. Template Engines

As well as REST web services, you can also use Spring WebFlux to serve dynamic HTML
content. Spring WebFlux supports a variety of templating technologies, including
Thymeleaf, FreeMarker, and Mustache.
Spring Boot includes auto-configuration support for the following templating engines:
7.2.5. Error Handling

Spring Boot provides a WebExceptionHandler that handles all errors in a sensible way.
Its position in the processing order is immediately before the handlers provided by
WebFlux, which are considered last. For machine clients, it produces a JSON response
with details of the error, the HTTP status, and the exception message. For browser
clients, there is a “whitelabel” error handler that renders the same data in HTML
format. You can also provide your own HTML templates to display errors (see the
next section).
The first step to customizing this feature often involves using the existing mechanism
but replacing or augmenting the error contents. For that, you can add a bean of type
ErrorAttributes.
To change the error handling behavior, you can implement ErrorWebExceptionHandler and
register a bean definition of that type. Because a WebExceptionHandler is quite
low-level, Spring Boot also provides a convenient AbstractErrorWebExceptionHandler to
let you handle errors in a WebFlux functional way, as shown in the following example:




    

public class CustomErrorWebExceptionHandler extends AbstractErrorWebExceptionHandler {
    // Define constructor here
    @Override
    protected RouterFunction<ServerResponse> getRoutingFunction(ErrorAttributes errorAttributes) {
        return RouterFunctions
                .route(aPredicate, aHandler)
                .andRoute(anotherPredicate, anotherHandler);
For a more complete picture, you can also subclass DefaultErrorWebExceptionHandler
directly and override specific methods.
Custom Error Pages

If you want to display a custom HTML error page for a given status code, you can add a
file to an /error folder. Error pages can either be static HTML (that is, added under
any of the static resource folders) or built with templates. The name of the file should
be the exact status code or a series mask.
For example, to map 404 to a static HTML file, your folder structure would be as
follows:
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- public/
             +- error/
             |   +- 404.html
             +- <other public assets>

To map all 5xx errors by using a Mustache template, your folder structure would be as
follows:
 +- main/
     +- java/
     |   + <source code>
     +- resources/
         +- templates/
             +- error/
             |   +- 5xx.mustache
             +- <other templates>

7.2.6. Web Filters

Spring WebFlux provides a WebFilter interface that can be implemented to filter HTTP
request-response exchanges. WebFilter beans found in the application context will
be automatically used to filter each exchange.
Where the order of the filters is important they can implement Ordered or be annotated
with @Order. Spring Boot auto-configuration may configure web filters for you. When it
does so, the orders shown in the following table will be used:
7.3. JAX-RS and Jersey

If you prefer the JAX-RS programming model for REST endpoints, you can use one of the
available implementations instead of Spring MVC. Jersey and
Apache CXF work quite well out of the box. CXF requires you to
register its Servlet or Filter as a @Bean in your application context. Jersey has
some native Spring support, so we also provide auto-configuration support for it in
Spring Boot, together with a starter.
To get started with Jersey, include the spring-boot-starter-jersey as a dependency
and then you need one @Bean of type ResourceConfig in which you register all the
endpoints, as shown in the following example:
@Component
public class JerseyConfig extends ResourceConfig {
    public JerseyConfig() {
        register(Endpoint.class);
Jersey’s support for scanning executable archives is rather limited. For example,
it cannot scan for endpoints in a package found in a fully executable jar file or in WEB-INF/classes when running an executable war file.
To avoid this limitation, the packages method should not be used, and endpoints should
be registered individually by using the register method, as shown in the preceding
example.
For more advanced customizations, you can also register an arbitrary number of beans that
implement ResourceConfigCustomizer.
All the registered endpoints should be @Components with HTTP resource annotations
(@GET and others), as shown in the following example:
@Component
@Path("/hello")
public class Endpoint {
    public String message() {
        return "Hello";
Since the Endpoint is a Spring @Component, its lifecycle is managed by Spring and you
can use the @Autowired annotation to inject dependencies and use the @Value
annotation to inject external configuration. By default, the Jersey servlet is registered
and mapped to /*. You can change the mapping by adding @ApplicationPath to your
ResourceConfig.
By default, Jersey is set up as a Servlet in a @Bean of type ServletRegistrationBean
named jerseyServletRegistration. By default, the servlet is initialized lazily, but you
can customize that behavior by setting spring.jersey.servlet.load-on-startup. You can
disable or override that bean by creating one of your own with the same name. You can
also use a filter instead of a servlet by setting spring.jersey.type=filter (in which
case, the @Bean to replace or override is jerseyFilterRegistration). The filter has
an @Order, which you can set with spring.jersey.filter.order. Both the servlet and
the filter registrations can be given init parameters by using spring.jersey.init.* to
specify a map of properties.
7.4. Embedded Servlet Container Support

Spring Boot includes support for embedded Tomcat,
Jetty, and
Undertow servers. Most developers use the
appropriate “Starter” to obtain a fully configured instance. By default, the embedded
server listens for HTTP requests on port 8080.
7.4.1. Servlets, Filters, and listeners

When using an embedded servlet container, you can register servlets, filters, and all the
listeners (such as HttpSessionListener) from the Servlet spec, either by using Spring
beans or by scanning for Servlet components.
Registering Servlets, Filters, and Listeners as Spring Beans

Any Servlet, Filter, or servlet *Listener instance that is a Spring bean is
registered with the embedded container. This can be particularly convenient if you want
to refer to a value from your application.properties during configuration.
By default, if the context contains only a single Servlet, it is mapped to /. In the
case of multiple servlet beans, the bean name is used as a path prefix. Filters map to
If convention-based mapping is not flexible enough, you can use the
ServletRegistrationBean, FilterRegistrationBean, and
ServletListenerRegistrationBean classes for complete control.
Filter beans can be ordered to control their position in the filter chain by using
@Order or implemented Ordered. It is usually safe to leave Filter beans unordered.
However, if a specific order is required, you should avoid configuring a Filter that reads
the request body at Ordered.HIGHEST_PRECEDENCE, since it might go against the character
encoding configuration of your application. If a Servlet filter wraps the request, it
should be configured with an order that is less than or equal to
OrderedFilter.REQUEST_WRAPPER_FILTER_MAX_ORDER.
To see the order of every Filter in your application, enable debug level logging
for the web logging group
(logging.level.web=debug). Details of the registered filters, including their order and
URL patterns, will then be logged at startup.
7.4.2. Servlet Context Initialization

Embedded servlet containers do not directly execute the Servlet 3.0+
javax.servlet.ServletContainerInitializer interface or Spring’s
org.springframework.web.WebApplicationInitializer interface. This is an intentional
design decision intended to reduce the risk that third party libraries designed to run
inside a war may break Spring Boot applications.
If you need to perform servlet context initialization in a Spring Boot application, you
should register a bean that implements the
org.springframework.boot.web.servlet.ServletContextInitializer interface. The
single onStartup method provides access to the ServletContext and, if necessary, can
easily be used as an adapter to an existing WebApplicationInitializer.
Scanning for Servlets, Filters, and listeners

When using an embedded container, automatic registration of classes annotated with
@WebServlet, @WebFilter, and @WebListener can be enabled by using
@ServletComponentScan.
7.4.3. The ServletWebServerApplicationContext

Under the hood, Spring Boot uses a different type of ApplicationContext for embedded
servlet container support.  The ServletWebServerApplicationContext is a special type of
WebApplicationContext that bootstraps itself by searching for a single
ServletWebServerFactory bean. Usually a TomcatServletWebServerFactory,
JettyServletWebServerFactory, or UndertowServletWebServerFactory
has been auto-configured.
You usually do not need to be aware of these implementation classes. Most
applications are auto-configured, and the appropriate ApplicationContext and
ServletWebServerFactory are created on your behalf.
7.4.4. Customizing Embedded Servlet Containers

Common servlet container settings can be configured by using Spring Environment
properties. Usually, you would define the properties in your application.properties
file.
Common server settings include:
Network settings: Listen port for incoming HTTP requests (server.port), interface
address to bind to server.address, and so on.
Session settings: Whether the session is persistent (server.servlet.session.persistent),
session timeout (server.servlet.session.timeout), location of session data
(server.servlet.session.store-dir), and session-cookie configuration
(server.servlet.session.cookie.*).
Error management: Location of the error page (server.error.path) and so on.
HTTP compression
Spring Boot tries as much as possible to expose common settings, but this is not always
possible. For those cases, dedicated namespaces offer server-specific customizations (see
server.tomcat and server.undertow). For instance,
access logs can be configured with specific
features of the embedded servlet container.
Programmatic Customization

If you need to programmatically configure your embedded servlet container, you can
register a Spring bean that implements the WebServerFactoryCustomizer interface.
WebServerFactoryCustomizer provides access to the
ConfigurableServletWebServerFactory, which includes numerous customization setter
methods. The following example shows programmatically setting the port:
import org.springframework.boot.web.server.WebServerFactoryCustomizer;
import org.springframework.boot.web.servlet.server.ConfigurableServletWebServerFactory;
import org.springframework.stereotype.Component;
@Component
public class CustomizationBean implements WebServerFactoryCustomizer<ConfigurableServletWebServerFactory> {
    @Override
    public void customize(ConfigurableServletWebServerFactory server) {
        server.setPort(9000);
TomcatServletWebServerFactory, JettyServletWebServerFactory and UndertowServletWebServerFactory
are dedicated variants of ConfigurableServletWebServerFactory that have additional customization setter methods
for Tomcat, Jetty and Undertow respectively.
Customizing ConfigurableServletWebServerFactory Directly

If the preceding customization techniques are too limited, you can register the
TomcatServletWebServerFactory, JettyServletWebServerFactory, or
UndertowServletWebServerFactory bean yourself.
@Bean
public ConfigurableServletWebServerFactory webServerFactory() {
    TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory();
    factory.setPort(9000);
    factory.setSessionTimeout(10, TimeUnit.MINUTES);
    factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND, "/notfound.html"));
    return factory;
Setters are provided for many configuration options. Several protected method “hooks”
are also provided should you need to do something more exotic. See the
source
code documentation for details.
7.4.5. JSP Limitations

When running a Spring Boot application that uses an embedded servlet container (and is
packaged as an executable archive), there are some limitations in the JSP support.
With Jetty and Tomcat, it should work if you use war packaging. An executable war will
work when launched with java -jar, and will also be deployable to any standard
container. JSPs are not supported when using an executable jar.
Undertow does not support JSPs.
Creating a custom error.jsp page does not override the default view for
error handling.
Custom error pages should be used
instead.
7.5. Embedded Reactive Server Support

Spring Boot includes support for the following embedded reactive web servers:
Reactor Netty, Tomcat, Jetty, and Undertow. Most developers use the appropriate “Starter”
to obtain a fully configured instance. By default, the embedded server listens for HTTP
requests on port 8080.




    

7.6. Reactive Server Resources Configuration

When auto-configuring a Reactor Netty or Jetty server, Spring Boot will create specific
beans that will provide HTTP resources to the server instance: ReactorResourceFactory
or JettyResourceFactory.
By default, those resources will be also shared with the Reactor Netty and Jetty clients
for optimal performances, given:
Developers can override the resource configuration for Jetty and Reactor Netty by providing
a custom ReactorResourceFactory or JettyResourceFactory bean - this will be applied to
both clients and servers.
You can learn more about the resource configuration on the client side in the
WebClient Runtime section.
RSocket is a binary protocol for use on byte stream transports.
It enables symmetric interaction models via async message passing over a single connection.
Spring Framework, with the Spring Messaging module supports RSocket both on the server and
the client side. On the server side, it lets you create special @Controller beans
to handle incoming RSocket messages.
Methods in your controller are mapped to RSocket routes by using @MessageMapping annotations.
The following code shows a typical @Controller:
@Controller
public class MyRSocketController {
    @MessageMapping("chat.room.{name}")
    public Flux<ChatMessages> enterChatRoom(@DestinationVariable String chatRoom,
            Flux<ChatMessages> messages) {
        // ...
    @MessageMapping("users.\{user}.info")
    Mono<ChatUserInfo> getUserInfo(@DestinationVariable String user) {
        // ...
8.1. RSocket Strategies Auto-configuration

Spring Boot auto-configures an RSocketStrategies bean that provides all the required
infrastructure for encoding and decoding RSocket payloads. By default, the
auto-configuration will try to configure the following (in order):
Developers can customize the RSocketStrategies component by creating beans that
implement the RSocketStrategiesCustomizer interface. Note that their @Order is
important, as it determines the order of codecs.
8.2. RSocket server Auto-configuration

Spring Boot provides auto-configuration for RSocket servers. The required dependencies
are provided by the spring-boot-starter-rsocket.
Spring Boot will start an RSocket server as a new embedded server in your application,
or will plug the RSocket infrastructure into an existing reactive Web server. This
depends on the type of application and its configuration.
In case of a WebFlux application (i.e. of type WebApplicationType.REACTIVE), the
RSocket server will be plugged into the existing Web Server only if the following
properties match:
spring.rsocket.server.mapping-path=/rsocket # a mapping path is defined
spring.rsocket.server.transport=websocket # websocket is chosen as a transport
#spring.rsocket.server.port= # no port is defined
The only other way to create an RSocket server is to start an independent, embedded
RSocket server. Besides the dependency requirements, the only required configuration
is to define a port for that server:
spring.rsocket.server.port=9898 # the only required configuration
spring.rsocket.server.transport=tcp # you're free to configure other properties
8.3. Spring Messaging RSocket support

Spring Boot will auto-configure the Spring Messaging infrastructure for RSocket.
An RSocketStrategies bean is created to provide encoding and decoding support
for RSocket messages. By default, Spring Boot will try to auto-configure JSON
support with Jackson for application/json and "application/*+json" media types.
Check out the Jackson support section to know more
about customization possibilities.
Developers can create RSocketStrategiesCustomizer beans to add other strategies,
assuming there are Encoder and Decoder implementations available.
8.4. Calling RSocket Services with RSocketRequester

Once the RSocket channel is established between server and client, any party can send or
receive requests to the other.
As a server, you can get injected an RSocketRequester instance on any handler method of
an RSocket @Controller. As a client, you need to configure and establish an RSocket
connection first. Spring Boot auto-configures an RSocketRequester.Builder for such cases
with the expected codecs.
The RSocketRequester.Builder instance is a prototype bean, meaning each injection point
will provide you with a new instance - this is done on purpose since this builder is stateful
and you shouldn’t create requesters with different setups using the same instance.
The following code shows a typical example:
@Service
public class MyService {
    private final RSocketRequester rsocketRequester;
    public MyService(RSocketRequester.Builder rsocketRequesterBuilder) {
        this.rsocketRequester = rsocketRequesterBuilder
                .connectTcp("example.org", 9090).block();
    public Mono<User> someRSocketCall(String name) {
        return this.requester.route("user").data(name)
                .retrieveMono(User.class);
If Spring Security is on the classpath, then web applications are
secured by default. Spring Boot relies on Spring Security’s content-negotiation strategy
to determine whether to use httpBasic or formLogin. To add method-level security to a
web application, you can also add @EnableGlobalMethodSecurity with your desired
settings. Additional information can be found in the
Spring Security Reference Guide.
The default UserDetailsService has a single user. The user name is user, and the
password is random and is printed at INFO level when the application starts, as shown in
the following example:
Using generated security password: 78fa095d-3f4c-48b1-ad50-e24c31d5cf35
If you fine-tune your logging configuration, ensure that the
org.springframework.boot.autoconfigure.security category is set to log INFO-level
messages. Otherwise, the default password is not printed.
You can change the username and password by providing a spring.security.user.name and
spring.security.user.password.
The basic features you get by default in a web application are:
A UserDetailsService (or ReactiveUserDetailsService in case of a WebFlux application)
bean with in-memory store and a single user with a generated password (see
SecurityProperties.User
for the properties of the user).
Form-based login or HTTP Basic security (depending on the Accept header in the request) for
the entire application (including actuator endpoints if actuator is on the classpath).
A DefaultAuthenticationEventPublisher for publishing authentication events.
9.1. MVC Security

The default security configuration is implemented in SecurityAutoConfiguration and
UserDetailsServiceAutoConfiguration. SecurityAutoConfiguration imports
SpringBootWebSecurityConfiguration for web security and
UserDetailsServiceAutoConfiguration configures authentication, which is also
relevant in non-web applications. To switch off the default web application security
configuration completely, you can add a bean of type WebSecurityConfigurerAdapter (doing
so does not disable the UserDetailsService configuration or Actuator’s security).
To also switch off the UserDetailsService configuration, you can add a bean of type
UserDetailsService, AuthenticationProvider, or AuthenticationManager.
Access rules can be overridden by adding a custom WebSecurityConfigurerAdapter. Spring
Boot provides convenience methods that can be used to override access rules for actuator
endpoints and static resources. EndpointRequest can be used to create a RequestMatcher
that is based on the management.endpoints.web.base-path property.
PathRequest can be used to create a RequestMatcher for resources in
commonly used locations.
9.2. WebFlux Security

Similar to Spring MVC applications, you can secure your WebFlux applications by adding
the spring-boot-starter-security dependency. The default security configuration is
implemented in ReactiveSecurityAutoConfiguration and
UserDetailsServiceAutoConfiguration. ReactiveSecurityAutoConfiguration imports
WebFluxSecurityConfiguration for web security and UserDetailsServiceAutoConfiguration
configures authentication, which is also relevant in non-web applications. To switch off the default web application security
configuration completely, you can add a bean of type WebFilterChainProxy (doing so does
not disable the UserDetailsService configuration or Actuator’s security).
To also switch off the UserDetailsService configuration, you can add a bean of type
ReactiveUserDetailsService or ReactiveAuthenticationManager.
Access rules can be configured by adding a custom SecurityWebFilterChain. Spring
Boot provides convenience methods that can be used to override access rules for actuator
endpoints and static resources. EndpointRequest can be used to create a
ServerWebExchangeMatcher that is based on the management.endpoints.web.base-path
property.
PathRequest can be used to create a ServerWebExchangeMatcher for resources in
commonly used locations.
For example, you can customize your security configuration by adding something like:
@Bean
public SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
    return http
        .authorizeExchange()
            .matchers(PathRequest.toStaticResources().atCommonLocations()).permitAll()
            .pathMatchers("/foo", "/bar")
                .authenticated().and()
            .formLogin().and()
        .build();
9.3.1. Client

If you have spring-security-oauth2-client on your classpath, you can take advantage of
some auto-configuration to make it easy to set up an OAuth2/Open ID Connect clients. This configuration
makes use of the properties under OAuth2ClientProperties. The same properties are applicable to both servlet and reactive applications.
You can register multiple OAuth2 clients and providers under the
spring.security.oauth2.client prefix, as shown in the following example:
spring.security.oauth2.client.registration.my-client-1.client-id=abcd
spring.security.oauth2.client.registration.my-client-1.client-secret=password
spring.security.oauth2.client.registration.my-client-1.client-name=Client for user scope
spring.security.oauth2.client.registration.my-client-1.provider=my-oauth-provider
spring.security.oauth2.client.registration.my-client-1.scope=user
spring.security.oauth2.client.registration.my-client-1.redirect-uri-template=https://my-redirect-uri.com
spring.security.oauth2.client.registration.my-client-1.client-authentication-method=basic
spring.security.oauth2.client.registration.my-client-1.authorization-grant-type=authorization_code
spring.security.oauth2.client.registration.my-client-2.client-id=abcd
spring.security.oauth2.client.registration.my-client-2.client-secret=password
spring.security.oauth2.client.registration.my-client-2.client-name=Client for email scope
spring.security.oauth2.client.registration.my-client-2.provider=my-oauth-provider
spring.security.oauth2.client.registration.my-client-2.scope=email
spring.security.oauth2.client.registration.my-client-2.redirect-uri-template=https://my-redirect-uri.com
spring.security.oauth2.client.registration.my-client-2.client-authentication-method=basic
spring.security.oauth2.client.registration.my-client-2.authorization-grant-type=authorization_code
spring.security.oauth2.client.provider.my-oauth-provider.authorization-uri=https://my-auth-server/oauth/authorize
spring.security.oauth2.client.provider.my-oauth-provider.token-uri=https://my-auth-server/oauth/token
spring.security.oauth2.client.provider.my-oauth-provider.user-info-uri=https://my-auth-server/userinfo
spring.security.oauth2.client.provider.my-oauth-provider.user-info-authentication-method=header
spring.security.oauth2.client.provider.my-oauth-provider.jwk-set-uri=https://my-auth-server/token_keys
spring.security.oauth2.client.provider.my-oauth-provider.user-name-attribute=name
For OpenID Connect providers that support OpenID Connect discovery,
the configuration can be further simplified. The provider needs to be configured with an issuer-uri which is the
URI that the it asserts as its Issuer Identifier. For example, if the
issuer-uri provided is "https://example.com", then an OpenID Provider Configuration Request
will be made to "https://example.com/.well-known/openid-configuration". The result is expected
to be an OpenID Provider Configuration Response. The following example shows how an OpenID Connect
Provider can be configured with the issuer-uri:
spring.security.oauth2.client.provider.oidc-provider.issuer-uri=https://dev-123456.oktapreview.com/oauth2/default/
By default, Spring Security’s OAuth2LoginAuthenticationFilter only processes URLs
matching /login/oauth2/code/*. If you want to customize the redirect-uri to
use a different pattern, you need to provide configuration to process that custom pattern.
For example, for servlet applications, you can add your own WebSecurityConfigurerAdapter that resembles the
following:
public class OAuth2LoginSecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
            .authorizeRequests()
                .anyRequest().authenticated()
                .and()
            .oauth2Login()
                .redirectionEndpoint()
                    .baseUri("/custom-callback");
OAuth2 client registration for common providers

For common OAuth2 and OpenID providers, including Google, Github, Facebook, and Okta,
we provide a set of provider defaults (google, github, facebook, and okta,
respectively).




    

If you do not need to customize these providers, you can set the provider attribute to
the one for which you need to infer defaults. Also, if the key for the client registration matches a
default supported provider, Spring Boot infers that as well.
In other words, the two configurations in the following example use the Google provider:
spring.security.oauth2.client.registration.my-client.client-id=abcd
spring.security.oauth2.client.registration.my-client.client-secret=password
spring.security.oauth2.client.registration.my-client.provider=google
spring.security.oauth2.client.registration.google.client-id=abcd
spring.security.oauth2.client.registration.google.client-secret=password
9.3.2. Resource Server

If you have spring-security-oauth2-resource-server on your classpath, Spring Boot can
set up an OAuth2 Resource Server. For JWT configuration, a JWK Set URI or OIDC Issuer URI
needs to be specified, as shown in the following examples:
spring.security.oauth2.resourceserver.jwt.jwk-set-uri=https://example.com/oauth2/default/v1/keys
If the authorization server does not support a JWK Set URI, you can configure the
resource server with the Public Key used for verifying the signature of the JWT. This can
be done using the spring.security.oauth2.resourceserver.jwt.public-key-location property,
where the value needs to point to a file containing the public key in the PEM-encoded x509
format.
Alternatively, you can define your own JwtDecoder bean for servlet applications
or a ReactiveJwtDecoder for reactive applications.
In cases where opaque tokens are used instead of JWTs, you can configure the following properties
to validate tokens via introspection:
spring.security.oauth2.resourceserver.opaquetoken.introspection-uri=https://example.com/check-token
spring.security.oauth2.resourceserver.opaquetoken.client-id=my-client-id
spring.security.oauth2.resourceserver.opaquetoken.client-secret-my-client-secret
Again, the same properties are applicable for both servlet and reactive applications.
Alternatively, you can define your own OAuth2TokenIntrospectionClient bean for servlet applications
or a ReactiveOAuth2TokenIntrospectionClient for reactive applications.
9.3.3. Authorization Server

Currently, Spring Security does not provide support for implementing an OAuth 2.0
Authorization Server. However, this functionality is available from
the Spring Security OAuth project,
which will eventually be superseded by Spring Security completely. Until then, you can
use the spring-security-oauth2-autoconfigure module to easily set up an OAuth 2.0 authorization server;
see its documentation for instructions.
9.4. Actuator Security

For security purposes, all actuators other than /health and /info are disabled by
default. The management.endpoints.web.exposure.include property can be used to enable
the actuators.
If Spring Security is on the classpath and no other WebSecurityConfigurerAdapter is
present, all actuators other than /health and /info are secured by Spring Boot
auto-configuration. If you define a custom WebSecurityConfigurerAdapter, Spring Boot
auto-configuration will back off and you will be in full control of actuator access rules.
Before setting the management.endpoints.web.exposure.include, ensure that the
exposed actuators do not contain sensitive information and/or are secured by placing them
behind a firewall or by something like Spring Security.
9.4.1. Cross Site Request Forgery Protection

Since Spring Boot relies on Spring Security’s defaults, CSRF protection is turned on by
default. This means that the actuator endpoints that require a POST (shutdown and
loggers endpoints), PUT or DELETE will get a 403 forbidden error when the default
security configuration is in use.
The Spring Framework provides extensive support for working with SQL
databases, from direct JDBC access using JdbcTemplate to complete “object relational
mapping” technologies such as Hibernate. Spring Data provides an
additional level of functionality: creating Repository implementations directly from
interfaces and using conventions to generate queries from your method names.
10.1. Configure a DataSource

Java’s javax.sql.DataSource interface provides a standard method of working with
database connections. Traditionally, a 'DataSource' uses a URL along with some
credentials to establish a database connection.
See the “How-to” section for more
advanced examples, typically to take full control over the configuration of the
DataSource.
10.1.1. Embedded Database Support

It is often convenient to develop applications by using an in-memory embedded database.
Obviously, in-memory databases do not provide persistent storage. You need to populate
your database when your application starts and be prepared to throw away data when your
application ends.
Spring Boot can auto-configure embedded H2,
HSQL, and Derby databases. You need not
provide any connection URLs. You need only include a build dependency to the embedded
database that you want to use.
If you are using this feature in your tests, you may notice that the same database is
reused by your whole test suite regardless of the number of application contexts that you
use. If you want to make sure that each context has a separate embedded database, you
should set spring.datasource.generate-unique-name to true.
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
    <groupId>org.hsqldb</groupId>
    <artifactId>hsqldb</artifactId>
    <scope>runtime</scope>
</dependency>
You need a dependency on spring-jdbc for an embedded database to be
auto-configured. In this example, it is pulled in transitively through
spring-boot-starter-data-jpa.
If, for whatever reason, you do configure the connection URL for an embedded
database, take care to ensure that the database’s automatic shutdown is disabled. If you
use H2, you should use DB_CLOSE_ON_EXIT=FALSE to do so. If you use HSQLDB, you should
ensure that shutdown=true is not used. Disabling the database’s automatic shutdown lets
Spring Boot control when the database is closed, thereby ensuring that it happens once
access to the database is no longer needed.
10.1.2. Connection to a Production Database

Production database connections can also be auto-configured by using a pooling
DataSource. Spring Boot uses the following algorithm for choosing a specific
implementation:
We prefer HikariCP for its performance and
concurrency. If HikariCP is available, we always choose it.
Otherwise, if the Tomcat pooling DataSource is available, we use it.
If neither HikariCP nor the Tomcat pooling datasource are available and if
Commons DBCP2 is available, we use it.
You can bypass that algorithm completely and specify the connection pool to use by
setting the spring.datasource.type property. This is especially important if you run
your application in a Tomcat container, as tomcat-jdbc is provided by default.
DataSource configuration is controlled by external configuration properties in
spring.datasource.*. For example, you might declare the following section in
application.properties:
spring.datasource.url=jdbc:mysql://localhost/test
spring.datasource.username=dbuser
spring.datasource.password=dbpass
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
For a pooling DataSource to be created, we need to be able to verify that a valid
Driver class is available, so we check for that before doing anything. In other words,
if you set spring.datasource.driver-class-name=com.mysql.jdbc.Driver, then that class
has to be loadable.
DataSourceProperties
for more of the supported options. These are the standard options that work regardless of
the actual implementation. It is also possible to fine-tune implementation-specific
settings by using their respective prefix (spring.datasource.hikari.*,
spring.datasource.tomcat.*, and spring.datasource.dbcp2.*). Refer to the
documentation of the connection pool implementation you are using for more details.
For instance, if you use the
Tomcat
connection pool, you could customize many additional settings, as shown in the following
example:
# Number of ms to wait before throwing an exception if no connection is available.
spring.datasource.tomcat.max-wait=10000
# Maximum number of active connections that can be allocated from this pool at the same time.
spring.datasource.tomcat.max-active=50
# Validate the connection before borrowing it from the pool.
spring.datasource.tomcat.test-on-borrow=true
10.1.3. Connection to a JNDI DataSource

If you deploy your Spring Boot application to an Application Server, you might want to
configure and manage your DataSource by using your Application Server’s built-in features
and access it by using JNDI.
The spring.datasource.jndi-name property can be used as an alternative to the
spring.datasource.url, spring.datasource.username, and spring.datasource.password
properties to access the DataSource from a specific JNDI location. For example, the
following section in application.properties shows how you can access a JBoss AS defined
DataSource:
spring.datasource.jndi-name=java:jboss/datasources/customers
10.2. Using JdbcTemplate

Spring’s JdbcTemplate and NamedParameterJdbcTemplate classes are auto-configured, and
you can @Autowire them directly into your own beans, as shown in the following example:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Component;
@Component
public class MyBean {
    private final JdbcTemplate jdbcTemplate;
    @Autowired
    public MyBean(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    // ...
You can customize some properties of the template by using the spring.jdbc.template.*
properties, as shown in the following example:
spring.jdbc.template.max-rows=500
The NamedParameterJdbcTemplate reuses the same JdbcTemplate instance behind the
scenes. If more than one JdbcTemplate is defined and no primary candidate exists, the
NamedParameterJdbcTemplate is not auto-configured.
10.3. JPA and Spring Data JPA

The Java Persistence API is a standard technology that lets you “map” objects to
relational databases. The spring-boot-starter-data-jpa POM provides a quick way to get
started. It provides the following key dependencies:
We do not go into too many details of JPA or Spring Data here. You can
follow the “Accessing Data with JPA”
guide from spring.io and read the Spring Data JPA and
Hibernate reference documentation.
10.3.1. Entity Classes

Traditionally, JPA “Entity” classes are specified in a persistence.xml file. With
Spring Boot, this file is not necessary and “Entity Scanning” is used instead. By
default, all packages below your main configuration class (the one annotated with
@EnableAutoConfiguration or @SpringBootApplication) are searched.
Any classes annotated with @Entity, @Embeddable, or @MappedSuperclass are
considered. A typical entity class resembles the following example:
package com.example.myapp.domain;
import java.io.Serializable;
import javax.persistence.*;
@Entity
public class City implements Serializable {
    @GeneratedValue
    private Long id;
    @Column(nullable = false)
    private String name;
    @Column(nullable = false)
    private String state;
    // ... additional members, often include @OneToMany mappings
    protected City() {
        // no-args constructor required by JPA spec
        // this one is protected since it shouldn't be used directly
    public City(String name, String state) {
        this.name = name;
        this.state = state;
    public String getName() {
        return this.name;
    public String getState() {
        return this.state;
    // ... etc
You can customize entity scanning locations by using the @EntityScan annotation.
See the “howto.html”
how-to.
10.3.2. Spring Data JPA Repositories

Spring Data JPA repositories are interfaces that you can define to
access data. JPA queries are created automatically from your method names. For example, a
CityRepository interface might declare a findAllByState(String state) method to find
all the cities in a given state.
For more complex queries, you can annotate your method with Spring Data’s
Query annotation.




    

Spring Data repositories usually extend from the
Repository or
CrudRepository
interfaces. If you use auto-configuration, repositories are searched from the package
containing your main configuration class (the one annotated with
@EnableAutoConfiguration or @SpringBootApplication) down.
The following example shows a typical Spring Data repository interface definition:
package com.example.myapp.domain;
import org.springframework.data.domain.*;
import org.springframework.data.repository.*;
public interface CityRepository extends Repository<City, Long> {
    Page<City> findAll(Pageable pageable);
    City findByNameAndStateAllIgnoringCase(String name, String state);
Spring Data JPA repositories support three different modes of bootstrapping: default,
deferred, and lazy. To enable deferred or lazy bootstrapping, set the
spring.data.jpa.repositories.bootstrap-mode to deferred or lazy respectively. When
using deferred or lazy bootstrapping, the auto-configured EntityManagerFactoryBuilder
will use the context’s AsyncTaskExecutor, if any, as the bootstrap executor. If more
than one exists, the one named applicationTaskExecutor will be used.
We have barely scratched the surface of Spring Data JPA. For complete details, see
the Spring Data JPA
reference documentation.
10.3.3. Creating and Dropping JPA Databases

By default, JPA databases are automatically created only if you use an embedded
database (H2, HSQL, or Derby). You can explicitly configure JPA settings by using
spring.jpa.* properties. For example, to create and drop tables you can add the
following line to your application.properties:
spring.jpa.hibernate.ddl-auto=create-drop
Hibernate’s own internal property name for this (if you happen to remember it
better) is hibernate.hbm2ddl.auto. You can set it, along with other Hibernate native
properties, by using spring.jpa.properties.* (the prefix is stripped before adding
them to the entity manager). The following line shows an example of setting JPA
properties for Hibernate:
The line in the preceding example passes a value of true for the
hibernate.globally_quoted_identifiers property to the Hibernate entity manager.
By default, the DDL execution (or validation) is deferred until the ApplicationContext
has started. There is also a spring.jpa.generate-ddl flag, but it is not used if
Hibernate auto-configuration is active, because the ddl-auto settings are more
fine-grained.
10.3.4. Open EntityManager in View

If you are running a web application, Spring Boot by default registers
OpenEntityManagerInViewInterceptor
to apply the “Open EntityManager in View” pattern, to allow for lazy loading in web
views. If you do not want this behavior, you should set spring.jpa.open-in-view to
false in your application.properties.
10.4. Spring Data JDBC

Spring Data includes repository support for JDBC and will automatically generate SQL for
the methods on CrudRepository. For more advanced queries, a @Query annotation is
provided.
Spring Boot will auto-configure Spring Data’s JDBC repositories when the necessary
dependencies are on the classpath. They can be added to your project with a single
dependency on spring-boot-starter-data-jdbc. If necessary, you can take control of
Spring Data JDBC’s configuration by adding the @EnableJdbcRepositories annotation or a
JdbcConfiguration subclass to your application.
The H2 database provides a
browser-based console that
Spring Boot can auto-configure for you. The console is auto-configured when the following
conditions are met:
If you are not using Spring Boot’s developer tools but would still like to make use
of H2’s console, you can configure the spring.h2.console.enabled property with a value
of true.
10.5.1. Changing the H2 Console’s Path

By default, the console is available at /h2-console. You can customize the console’s
path by using the spring.h2.console.path property.
jOOQ Object Oriented Querying (jOOQ) is a popular product from
Data Geekery which generates Java code from your
database and lets you build type-safe SQL queries through its fluent API. Both the
commercial and open source editions can be used with Spring Boot.
10.6.1. Code Generation

In order to use jOOQ type-safe queries, you need to generate Java classes from your
database schema. You can follow the instructions in the
jOOQ user manual. If you use the
jooq-codegen-maven plugin and you also use the spring-boot-starter-parent
“parent POM”, you can safely omit the plugin’s <version> tag. You can also use Spring
Boot-defined version variables (such as h2.version) to declare the plugin’s database
dependency. The following listing shows an example:
<plugin>
    <groupId>org.jooq</groupId>
    <artifactId>jooq-codegen-maven</artifactId>
    <executions>
    </executions>
    <dependencies>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <version>${h2.version}</version>
        </dependency>
    </dependencies>
    <configuration>
            <driver>org.h2.Driver</driver>
            <url>jdbc:h2:~/yourdatabase</url>
        </jdbc>
        <generator>
        </generator>
    </configuration>
</plugin>
10.6.2. Using DSLContext

The fluent API offered by jOOQ is initiated through the org.jooq.DSLContext interface.
Spring Boot auto-configures a DSLContext as a Spring Bean and connects it to your
application DataSource. To use the DSLContext, you can @Autowire it, as shown in
the following example:
@Component
public class JooqExample implements CommandLineRunner {
    private final DSLContext create;
    @Autowired
    public JooqExample(DSLContext dslContext) {
        this.create = dslContext;
public List<GregorianCalendar> authorsBornAfter1980() {
    return this.create.selectFrom(AUTHOR)
        .where(AUTHOR.DATE_OF_BIRTH.greaterThan(new GregorianCalendar(1980, 0, 1)))
        .fetch(AUTHOR.DATE_OF_BIRTH);
10.6.3. jOOQ SQL Dialect

Unless the spring.jooq.sql-dialect property has been configured, Spring Boot determines
the SQL dialect to use for your datasource. If Spring Boot could not detect the dialect,
it uses DEFAULT.
10.6.4. Customizing jOOQ

More advanced customizations can be achieved by defining your own @Bean definitions,
which is used when the jOOQ Configuration is created. You can define beans for the
following jOOQ Types:
Spring Data provides additional projects that help you access a variety of NoSQL
technologies, including:
MongoDB,
Neo4J,
Elasticsearch,
Solr,
Redis,
Gemfire,
Cassandra,
Couchbase and
LDAP.
Spring Boot provides auto-configuration for Redis, MongoDB, Neo4j, Elasticsearch, Solr
Cassandra, Couchbase, and LDAP. You can make use of the other projects, but you must
configure them yourself. Refer to the appropriate reference documentation at
projects.spring.io/spring-data.
11.1. Redis

Redis is a cache, message broker, and richly-featured key-value store.
Spring Boot offers basic auto-configuration for the
Lettuce and
Jedis client libraries and the abstractions on top
of them provided by Spring Data
Redis.
There is a spring-boot-starter-data-redis “Starter” for collecting the dependencies
in a convenient way. By default, it uses
Lettuce. That starter handles both
traditional and reactive applications.
11.1.1. Connecting to Redis

You can inject an auto-configured RedisConnectionFactory, StringRedisTemplate, or
vanilla RedisTemplate instance as you would any other Spring Bean. By default, the
instance tries to connect to a Redis server at localhost:6379. The following listing
shows an example of such a bean:
@Component
public class MyBean {
    private StringRedisTemplate template;
    @Autowired
    public MyBean(StringRedisTemplate template) {
        this.template = template;
    // ...
You can also register an arbitrary number of beans that implement
LettuceClientConfigurationBuilderCustomizer for more advanced customizations. If you
use Jedis, JedisClientConfigurationBuilderCustomizer is also available.
If you add your own @Bean of any of the auto-configured types, it replaces the default
(except in the case of RedisTemplate, when the exclusion is based on the bean name,
redisTemplate, not its type). By default, if commons-pool2 is on the classpath, you
get a pooled connection factory.
MongoDB is an open-source NoSQL document database that uses a
JSON-like schema instead of traditional table-based relational data. Spring Boot offers
several conveniences for working with MongoDB, including the
spring-boot-starter-data-mongodb and spring-boot-starter-data-mongodb-reactive
“Starters”.
11.2.1. Connecting to a MongoDB Database

To access Mongo databases, you can inject an auto-configured
org.springframework.data.mongodb.MongoDbFactory. By default, the instance tries to
connect to a MongoDB server at mongodb://localhost/test The following example shows how
to connect to a MongoDB database:
import org.springframework.data.mongodb.MongoDbFactory;
import com.mongodb.DB;
@Component
public class MyBean {
    private final MongoDbFactory mongo;
    @Autowired
    public MyBean(MongoDbFactory mongo) {
        this.mongo = mongo;
    // ...
    public void example() {
        DB db = mongo.getDb();
        // ...
You can set the spring.data.mongodb.uri property to change the URL and configure
additional settings such as the replica set, as shown in the following example:
spring.data.mongodb.uri=mongodb://user:[email protected]:12345,mongo2.example.com:23456/test
Alternatively, as long as you use Mongo 2.x, you can specify a host/port. For
example, you might declare the following settings in your application.properties:
spring.data.mongodb.host=mongoserver
spring.data.mongodb.port=27017
If you have defined your own MongoClient, it will be used to auto-configure a suitable
MongoDbFactory. Both com.mongodb.MongoClient and com.mongodb.client.MongoClient
are supported.
If you use the Mongo 3.0 Java driver, spring.data.mongodb.host and
spring.data.mongodb.port are not supported. In such cases, spring.data.mongodb.uri
should be used to provide all of the configuration.
If you do not use Spring Data Mongo, you can inject com.mongodb.MongoClient beans
instead of using MongoDbFactory. If you want to take complete control of establishing
the MongoDB connection, you can also declare your own MongoDbFactory or MongoClient
bean.
If you are using the reactive driver, Netty is required for SSL. The
auto-configuration configures this factory automatically if Netty is available and the
factory to use hasn’t been customized already.
Spring Data MongoDB provides a
MongoTemplate class that is very
similar in its design to Spring’s JdbcTemplate. As with JdbcTemplate, Spring Boot
auto-configures a bean for you to inject the template, as follows:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.stereotype.Component;
@Component
public class MyBean {
    private final MongoTemplate mongoTemplate;
    @Autowired
    public MyBean(MongoTemplate mongoTemplate) {
        this.mongoTemplate = mongoTemplate;
    // ...
See the
MongoOperations
Javadoc for complete details.
11.2.3. Spring Data MongoDB Repositories

Spring Data includes repository support for MongoDB. As with the JPA repositories
discussed earlier, the basic principle is that queries are constructed automatically,
based on method names.
In fact, both Spring Data JPA and Spring Data MongoDB share the same common
infrastructure. You could take the JPA example from earlier and, assuming that City is
now a Mongo data class rather than a JPA @Entity, it works in the same way, as shown
in the following example:




    

package com.example.myapp.domain;
import org.springframework.data.domain.*;
import org.springframework.data.repository.*;
public interface CityRepository extends Repository<City, Long> {
    Page<City> findAll(Pageable pageable);
    City findByNameAndStateAllIgnoringCase(String name, String state);
For complete details of Spring Data MongoDB, including its rich object mapping
technologies, refer to its reference
documentation.
Spring Boot offers auto-configuration for
Embedded Mongo. To use it in
your Spring Boot application, add a dependency on
de.flapdoodle.embed:de.flapdoodle.embed.mongo.
The port that Mongo listens on can be configured by setting the spring.data.mongodb.port
property. To use a randomly allocated free port, use a value of 0. The MongoClient
created by MongoAutoConfiguration is automatically configured to use the randomly
allocated port.
If you have SLF4J on the classpath, the output produced by Mongo is automatically routed
to a logger named org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongo.
You can declare your own IMongodConfig and IRuntimeConfig beans to take control of
the Mongo instance’s configuration and logging routing. The download configuration can be
customized by declaring a DownloadConfigBuilderCustomizer bean.
Neo4j is an open-source NoSQL graph database that uses a rich data
model of nodes connected by first class relationships, which is better suited for
connected big data than traditional RDBMS approaches. Spring Boot offers several
conveniences for working with Neo4j, including the spring-boot-starter-data-neo4j
“Starter”.
11.3.1. Connecting to a Neo4j Database

To access a Neo4j server, you can inject an auto-configured
org.neo4j.ogm.session.Session. By default, the instance tries to connect to a Neo4j
server at localhost:7687 using the Bolt protocol. The following example shows how to
inject a Neo4j Session:
@Component
public class MyBean {
    private final Session session;
    @Autowired
    public MyBean(Session session) {
        this.session = session;
    // ...
You can configure the uri and credentials to use by setting the spring.data.neo4j.*
properties, as shown in the following example:
spring.data.neo4j.uri=bolt://my-server:7687
spring.data.neo4j.username=neo4j
spring.data.neo4j.password=secret
You can take full control over the session creation by either adding a
org.neo4j.ogm.config.Configuration bean or a org.neo4j.ogm.session.SessionFactory
bean.
11.3.2. Using the Embedded Mode

If you add org.neo4j:neo4j-ogm-embedded-driver to the dependencies of your application,
Spring Boot automatically configures an in-process embedded instance of Neo4j that does
not persist any data when your application shuts down.
As the embedded Neo4j OGM  driver  does not provide the Neo4j kernel itself, you have
to declare org.neo4j:neo4j as dependency yourself. Refer to
Neo4j OGM documentation for a list of compatible versions.
The embedded driver takes precedence over the other drivers when there are multiple
drivers on the classpath. You can explicitly disable the embedded mode by setting
spring.data.neo4j.embedded.enabled=false.
Data Neo4j Tests
automatically make use of an embedded Neo4j instance if the embedded driver and Neo4j
kernel are on the classpath as described above.
11.3.3. Using Native Types

Neo4j-OGM can map some types, like those in java.time.*, to String-based properties
or to one of the native types that Neo4j provides. For backwards compatibility reasons
the default for Neo4j-OGM is to use a String-based representation. To use native types,
add a dependency on either org.neo4j:neo4j-ogm-bolt-native-types or
org.neo4j:neo4j-ogm-embedded-native-types, and configure the
spring.data.neo4j.use-native-types property as shown in the following example:
spring.data.neo4j.use-native-types=true
11.3.4. Neo4jSession

By default, if you are running a web application, the session is bound to the thread for
the entire processing of the request (that is, it uses the "Open Session in View"
pattern). If you do not want this behavior, add the following line to your
application.properties file:
spring.data.neo4j.open-in-view=false
Spring Data Neo4j shares the common infrastructure with Spring Data JPA as many other
Spring Data modules do. You could take the JPA example from earlier and define
City as Neo4j OGM @NodeEntity rather than JPA @Entity and the repository
abstraction works in the same way, as shown in the following example:
package com.example.myapp.domain;
import java.util.Optional;
import org.springframework.data.neo4j.repository.*;
public interface CityRepository extends Neo4jRepository<City, Long> {
    Optional<City> findOneByNameAndState(String name, String state);
The spring-boot-starter-data-neo4j “Starter” enables the repository support as well
as transaction management. You can customize the locations to look for repositories and
entities by using @EnableNeo4jRepositories and @EntityScan respectively on a
@Configuration-bean.
For complete details of Spring Data Neo4j, including its object mapping
technologies, refer to the reference
documentation.
Spring Data Gemfire provides
convenient Spring-friendly tools for accessing the
Pivotal Gemfire data management
platform. There is a spring-boot-starter-data-gemfire “Starter” for collecting the
dependencies in a convenient way. There is currently no auto-configuration support for
Gemfire, but you can enable Spring Data Repositories with a
single annotation: @EnableGemfireRepositories.
11.5. Solr

Apache Solr is a search engine. Spring Boot offers basic
auto-configuration for the Solr 5 client library and the abstractions on top of it
provided by Spring Data Solr. There
is a spring-boot-starter-data-solr “Starter” for collecting the dependencies in a
convenient way.
11.5.1. Connecting to Solr

You can inject an auto-configured SolrClient instance as you would any other Spring
bean. By default, the instance tries to connect to a server at
localhost:8983/solr. The following example shows how to inject a Solr bean:

@Component
public class MyBean {
    private SolrClient solr;
    @Autowired
    public MyBean(SolrClient solr) {
        this.solr = solr;
    // ...
If you add your own @Bean of type SolrClient, it replaces the default.
11.5.2. Spring Data Solr Repositories

Spring Data includes repository support for Apache Solr. As with the JPA repositories
discussed earlier, the basic principle is that queries are automatically constructed for \
you based on method names.
In fact, both Spring Data JPA and Spring Data Solr share the same common infrastructure.
You could take the JPA example from earlier and, assuming that City is now a
@SolrDocument class rather than a JPA @Entity, it works in the same way.
Elasticsearch is an open source,
distributed, RESTful search and analytics engine. Spring Boot offers basic
auto-configuration for Elasticsearch.
Spring Boot supports several clients:
The transport client is still available but its support has been deprecated in
Spring Data Elasticsearch
and Elasticsearch itself. It will be removed in a future release.
Spring Boot provides a dedicated “Starter”, spring-boot-starter-data-elasticsearch.
The Jest client has been deprecated as well, since
both Elasticsearch and Spring Data Elasticsearch provide official support for REST clients.
11.6.1. Connecting to Elasticsearch using REST clients

Elasticsearch ships
two different REST clients
that you can use to query a cluster: the "Low Level" client and the "High Level" client.
If you have the org.elasticsearch.client:elasticsearch-rest-client dependency on the
classpath, Spring Boot will auto-configure and register a RestClient bean that
by default targets localhost:9200.
You can further tune how RestClient is configured, as shown in the following example:
spring.elasticsearch.rest.uris=https://search.example.com:9200
spring.elasticsearch.rest.read-timeout=10s
spring.elasticsearch.rest.username=user
spring.elasticsearch.rest.password=secret
You can also register an arbitrary number of beans that implement
RestClientBuilderCustomizer for more advanced customizations.
To take full control over the registration, define a RestClient bean.
If you have the org.elasticsearch.client:elasticsearch-rest-high-level-client dependency
on the classpath, Spring Boot will auto-configure a RestHighLevelClient, which wraps
any existing RestClient bean, reusing its HTTP configuration.
11.6.2. Connecting to Elasticsearch using Reactive REST clients

Spring Data Elasticsearch ships ReactiveElasticsearchClient
for querying Elasticsearch instances in a reactive fashion. It is built on top of WebFlux’s
WebClient, so both spring-boot-starter-elasticsearch and spring-boot-starter-webflux
dependencies are useful to enable this support.
By default, Spring Boot will auto-configure and register a ReactiveElasticsearchClient
bean that targets localhost:9200.
You can further tune how it is configured, as shown in the following example:
spring.elasticsearch.reactive.endpoints=search.example.com:9200
spring.elasticsearch.reactive.use-ssl=true
spring.elasticsearch.reactive.socket-timeout=10s
spring.elasticsearch.reactive.username=user
spring.elasticsearch.reactive.password=secret
If the configuration properties are not enough and you’d like to fully control the client
configuration, you can register a custom ClientConfiguration bean.
11.6.3. Connecting to Elasticsearch using Jest

Now that Spring Boot supports the official RestHighLevelClient, Jest support is
deprecated.
If you have Jest on the classpath, you can inject an auto-configured JestClient that
by default targets localhost:9200. You can further tune how the client is
configured, as shown in the following example:

spring.elasticsearch.jest.uris=https://search.example.com:9200
spring.elasticsearch.jest.read-timeout=10000
spring.elasticsearch.jest.username=user
spring.elasticsearch.jest.password=secret
You can also register an arbitrary number of beans that implement
HttpClientConfigBuilderCustomizer for more advanced customizations. The following
example tunes additional HTTP settings:
static class HttpSettingsCustomizer implements HttpClientConfigBuilderCustomizer {
    @Override
    public void customize(HttpClientConfig.Builder builder) {
        builder.maxTotalConnection(100).defaultMaxTotalConnectionPerRoute(5);
To take full control over the registration, define a JestClient bean.
11.6.4. Connecting to Elasticsearch by Using Spring Data

To connect to Elasticsearch, a RestHighLevelClient bean must be defined,
auto-configured by Spring Boot or manually provided by the application (see previous sections).
With this configuration in place, an
ElasticsearchRestTemplate can be injected like any other Spring bean,
as shown in the following example:
@Component
public class MyBean {
    private final ElasticsearchRestTemplate template;
    public MyBean(ElasticsearchRestTemplate template) {
        this.template = template;
    // ...
In the presence of spring-data-elasticsearch and the required dependencies
for using a WebClient (typically spring-boot-starter-webflux), Spring Boot can also
auto-configure a
ReactiveElasticsearchClient
and a ReactiveElasticsearchTemplate as beans. They are the reactive equivalent of the
other REST clients.
11.6.5. Spring Data Elasticsearch Repositories

Spring Data includes repository support for Elasticsearch. As with the JPA repositories
discussed earlier, the basic principle is that queries are constructed for you
automatically based on method names.




    

In fact, both Spring Data JPA and Spring Data Elasticsearch share the same common
infrastructure. You could take the JPA example from earlier and, assuming that City is
now an Elasticsearch @Document class rather than a JPA @Entity, it works in the same
Spring Boot supports both classic and reactive Elasticsearch repositories, using the
ElasticsearchRestTemplate or ReactiveElasticsearchTemplate beans. Most likely those
beans are auto-configured by Spring Boot given the required dependencies are present.
If you wish to use your own template for backing the Elasticsearch repositories, you can
add your own ElasticsearchRestTemplate or ElasticsearchOperations @Bean,
as long as it is named "elasticsearchTemplate". Same applies to
ReactiveElasticsearchTemplate and ReactiveElasticsearchOperations, with the bean
name "reactiveElasticsearchTemplate".
You can choose to disable the repositories support with the following property:
spring.data.elasticsearch.repositories.enabled=false
Cassandra is an open source, distributed database
management system designed to handle large amounts of data across many commodity servers.
Spring Boot offers auto-configuration for Cassandra and the abstractions on top of it
provided by Spring Data
Cassandra. There is a spring-boot-starter-data-cassandra “Starter” for collecting
the dependencies in a convenient way.
11.7.1. Connecting to Cassandra

You can inject an auto-configured CassandraTemplate or a Cassandra Session instance
as you would with any other Spring Bean. The spring.data.cassandra.* properties can be
used to customize the connection. Generally, you provide keyspace-name and
contact-points properties, as shown in the following example:
spring.data.cassandra.keyspace-name=mykeyspace
spring.data.cassandra.contact-points=cassandrahost1,cassandrahost2
You can also register an arbitrary number of beans that implement
ClusterBuilderCustomizer for more advanced customizations.
The following code listing shows how to inject a Cassandra bean:
@Component
public class MyBean {
    private CassandraTemplate template;
    @Autowired
    public MyBean(CassandraTemplate template) {
        this.template = template;
    // ...
If you add your own @Bean of type CassandraTemplate, it replaces the default.
11.7.2. Spring Data Cassandra Repositories

Spring Data includes basic repository support for Cassandra. Currently, this is more
limited than the JPA repositories discussed earlier and needs to annotate finder methods
with @Query.
Couchbase is an open-source, distributed, multi-model NoSQL
document-oriented database that is optimized for interactive applications. Spring Boot
offers auto-configuration for Couchbase and the abstractions on top of it provided by
Spring Data Couchbase. There are
spring-boot-starter-data-couchbase and spring-boot-starter-data-couchbase-reactive
“Starters” for collecting the dependencies in a convenient way.
11.8.1. Connecting to Couchbase

You can get a Bucket and Cluster by adding the Couchbase SDK and some configuration.
The spring.couchbase.* properties can be used to customize the connection. Generally,
you provide the bootstrap hosts, bucket name, and password, as shown in the following
example:
spring.couchbase.bootstrap-hosts=my-host-1,192.168.1.123
spring.couchbase.bucket.name=my-bucket
spring.couchbase.bucket.password=secret
You need to provide at least the bootstrap host(s), in which case the bucket name is
default and the password is an empty String. Alternatively, you can define your own
org.springframework.data.couchbase.config.CouchbaseConfigurer @Bean to take control
over the whole configuration.
It is also possible to customize some of the CouchbaseEnvironment settings. For
instance, the following configuration changes the timeout to use to open a new Bucket
and enables SSL support:
spring.couchbase.env.timeouts.connect=3000
spring.couchbase.env.ssl.key-store=/location/of/keystore.jks
spring.couchbase.env.ssl.key-store-password=secret
Check the spring.couchbase.env.* properties for more details.
11.8.2. Spring Data Couchbase Repositories

Spring Data includes repository support for Couchbase. For complete details of Spring
Data Couchbase, refer to the
reference
documentation.
You can inject an auto-configured CouchbaseTemplate instance as you would with any
other Spring Bean, provided a default CouchbaseConfigurer is available (which
happens when you enable Couchbase support, as explained earlier).
The following examples shows how to inject a Couchbase bean:
@Component
public class MyBean {
    private final CouchbaseTemplate template;
    @Autowired
    public MyBean(CouchbaseTemplate template) {
        this.template = template;
    // ...
There are a few beans that you can define in your own configuration to override those
provided by the auto-configuration:
To avoid hard-coding those names in your own config, you can reuse BeanNames provided
by Spring Data Couchbase. For instance, you can customize the converters to use, as
follows:
@Configuration(proxyBeanMethods = false)
public class SomeConfiguration {
    @Bean(BeanNames.COUCHBASE_CUSTOM_CONVERSIONS)
    public CustomConversions myCustomConversions() {
        return new CustomConversions(...);
    // ...
If you want to fully bypass the auto-configuration for Spring Data Couchbase,
provide your own implementation of
org.springframework.data.couchbase.config.AbstractCouchbaseDataConfiguration.
LDAP (Lightweight
Directory Access Protocol) is an open, vendor-neutral, industry standard application
protocol for accessing and maintaining distributed directory information services over an
IP network. Spring Boot offers auto-configuration for any compliant LDAP server as well
as support for the embedded in-memory LDAP server from
UnboundID.
LDAP abstractions are provided by
Spring Data LDAP.
There is a spring-boot-starter-data-ldap “Starter” for collecting the dependencies in
a convenient way.
11.9.1. Connecting to an LDAP Server

To connect to an LDAP server, make sure you declare a dependency on the
spring-boot-starter-data-ldap “Starter” or spring-ldap-core and then declare the
URLs of your server in your application.properties, as shown in the following example:
spring.ldap.urls=ldap://myserver:1235
spring.ldap.username=admin
spring.ldap.password=secret
If you need to customize connection settings, you can use the spring.ldap.base and
spring.ldap.base-environment properties.
An LdapContextSource is auto-configured based on these settings. If you need to customize
it, for instance to use a PooledContextSource, you can still inject the auto-configured
LdapContextSource. Make sure to flag your customized ContextSource as @Primary so
that the auto-configured LdapTemplate uses it.
11.9.2. Spring Data LDAP Repositories

Spring Data includes repository support for LDAP. For complete details of Spring
Data LDAP, refer to the
reference
documentation.
You can also inject an auto-configured LdapTemplate instance as you would with any
other Spring Bean, as shown in the following example:
@Component
public class MyBean {
    private final LdapTemplate template;
    @Autowired
    public MyBean(LdapTemplate template) {
        this.template = template;
    // ...
11.9.3. Embedded In-memory LDAP Server

For testing purposes, Spring Boot supports auto-configuration of an in-memory LDAP server
from UnboundID. To configure the server,
add a dependency to com.unboundid:unboundid-ldapsdk and declare a base-dn property, as
follows:
spring.ldap.embedded.base-dn=dc=spring,dc=io
It is possible to define multiple base-dn values, however, since distinguished names
usually contain commas, they must be defined using the correct notation.
In yaml files, you can use the yaml list notation:
spring.ldap.embedded.base-dn:
  - dc=spring,dc=io
  - dc=pivotal,dc=io
In properties files, you must include the index as part of the property name:
spring.ldap.embedded.base-dn[0]=dc=spring,dc=io
spring.ldap.embedded.base-dn[1]=dc=pivotal,dc=io
By default, the server starts on a random port and triggers the regular LDAP support.
There is no need to specify a spring.ldap.urls property.
If there is a schema.ldif file on your classpath, it is used to initialize the server.
If you want to load the initialization script from a different resource, you can also use
the spring.ldap.embedded.ldif property.
By default, a standard schema is used to validate LDIF files. You can turn off
validation altogether by setting the spring.ldap.embedded.validation.enabled property.
If you have custom attributes, you can use spring.ldap.embedded.validation.schema to
define your custom attribute types or object classes.
InfluxDB is an open-source time series database optimized
for fast, high-availability storage and retrieval of time series data in fields such as
operations monitoring, application metrics, Internet-of-Things sensor data, and real-time
analytics.
11.10.1. Connecting to InfluxDB

Spring Boot auto-configures an InfluxDB instance, provided the influxdb-java client
is on the classpath and the URL of the database is set, as shown in the following
example:
spring.influx.url=https://172.0.0.1:8086
If the connection to InfluxDB requires a user and password, you can set the
spring.influx.user and spring.influx.password properties accordingly.
InfluxDB relies on OkHttp. If you need to tune the http client InfluxDB uses behind the
scenes, you can register an InfluxDbOkHttpClientBuilderProvider bean.
The Spring Framework provides support for transparently adding caching to an application.
At its core, the abstraction applies caching to methods, thus reducing the number of
executions based on the information available in the cache. The caching logic is applied
transparently, without any interference to the invoker.  Spring Boot auto-configures the
cache infrastructure as long as caching support is enabled via the @EnableCaching
annotation.
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Component;
@Component
public class MathService {
    @Cacheable("piDecimals")
    public int computePiDecimal(int i) {
        // ...
This example demonstrates the use of caching on a potentially costly operation. Before
invoking computePiDecimal, the abstraction looks for an entry in the piDecimals cache
that matches the i argument. If an entry is found, the content in the cache is
immediately returned to the caller, and the method is not invoked. Otherwise, the method
is invoked, and the cache is updated before returning the value.
You can also use the standard JSR-107 (JCache) annotations (such as
@CacheResult) transparently. However, we strongly advise you to not mix and match the
Spring Cache and JCache annotations.
If you do not add any specific cache library, Spring Boot auto-configures a
simple provider that uses concurrent maps in
memory. When a cache is required (such as piDecimals in the preceding example), this
provider creates it for you. The simple provider is not really recommended for
production usage, but it is great for getting started and making sure that you understand
the features. When you have made up your mind about the cache provider to use, please
make sure to read its documentation to figure out how to configure the caches that your
application uses. Nearly all providers require you to explicitly configure every cache
that you use in the application. Some offer a way to customize the default caches defined
by the spring.cache.cache-names property.
12.1. Supported Cache Providers

The cache abstraction does not provide an actual store and relies on abstraction
materialized by the org.springframework.cache.Cache and
org.springframework.cache.CacheManager interfaces.
If you have not defined a bean of type CacheManager or a CacheResolver named
cacheResolver (see
CachingConfigurer),
Spring Boot tries to detect the following providers (in the indicated order):
It is also possible to force a particular cache provider by setting the
spring.cache.type property. Use this property if you need to
disable caching altogether in certain environment
(such as tests).
Use the spring-boot-starter-cache “Starter” to quickly add basic caching
dependencies. The starter brings in spring-context-support. If you add dependencies
manually, you must include spring-context-support in order to use the JCache,
EhCache 2.x, or Caffeine support.
If the CacheManager is auto-configured by Spring Boot, you can further tune its
configuration before it is fully initialized by exposing a bean that implements the
CacheManagerCustomizer interface. The following example sets a flag to say that null
values should be passed down to the underlying map:




    

@Bean
public CacheManagerCustomizer<ConcurrentMapCacheManager> cacheManagerCustomizer() {
    return new CacheManagerCustomizer<ConcurrentMapCacheManager>() {
        @Override
        public void customize(ConcurrentMapCacheManager cacheManager) {
            cacheManager.setAllowNullValues(false);
In the preceding example, an auto-configured ConcurrentMapCacheManager is expected. If
that is not the case (either you provided your own config or a different cache provider
was auto-configured), the customizer is not invoked at all. You can have as many
customizers as you want, and you can also order them by using @Order or Ordered.
Generic caching is used if the context defines at least one
org.springframework.cache.Cache bean. A CacheManager wrapping all beans of that type
is created.
12.1.2. JCache (JSR-107)

JCache is bootstrapped through the presence of a
javax.cache.spi.CachingProvider on the classpath (that is, a JSR-107 compliant caching
library exists on the classpath), and the JCacheCacheManager is provided by the
spring-boot-starter-cache “Starter”. Various compliant libraries are available, and
Spring Boot provides dependency management for Ehcache 3, Hazelcast, and Infinispan. Any
other compliant library can be added as well.
It might happen that more than one provider is present, in which case the provider must
be explicitly specified. Even if the JSR-107 standard does not enforce a standardized way
to define the location of the configuration file, Spring Boot does its best to
accommodate setting a cache with implementation details, as shown in the following
example:
# Only necessary if more than one provider is present
spring.cache.jcache.provider=com.acme.MyCachingProvider
spring.cache.jcache.config=classpath:acme.xml
When a cache library offers both a native implementation and JSR-107 support,
Spring Boot prefers the JSR-107 support, so that the same features are available if you
switch to a different JSR-107 implementation.
Spring Boot has general support for Hazelcast. If a
single HazelcastInstance is available, it is automatically reused for the
CacheManager as well, unless the spring.cache.jcache.config property is specified.
Caches can be created on startup by setting the spring.cache.cache-names property. If
a custom javax.cache.configuration.Configuration bean is defined, it is used to
customize them.
org.springframework.boot.autoconfigure.cache.JCacheManagerCustomizer beans are
invoked with the reference of the CacheManager for full customization.
If a standard javax.cache.CacheManager bean is defined, it is wrapped
automatically in an org.springframework.cache.CacheManager implementation that the
abstraction expects. No further customization is applied to it.
EhCache 2.x is used if a file named ehcache.xml can be found at
the root of the classpath. If EhCache 2.x is found, the EhCacheCacheManager provided by
the spring-boot-starter-cache “Starter” is used to bootstrap the cache manager. An
alternate configuration file can be provided as well, as shown in the following example:
spring.cache.ehcache.config=classpath:config/another-config.xml
Spring Boot has general support for Hazelcast. If a
HazelcastInstance has been auto-configured, it is automatically wrapped in a
CacheManager.
12.1.5. Infinispan

Infinispan has no default configuration file location, so it must
be specified explicitly. Otherwise, the default bootstrap is used.
spring.cache.infinispan.config=infinispan.xml
Caches can be created on startup by setting the spring.cache.cache-names property. If a
custom ConfigurationBuilder bean is defined, it is used to customize the caches.
The support of Infinispan in Spring Boot is restricted to the embedded mode and is quite
basic. If you want more options, you should use the official Infinispan Spring Boot
starter instead. See
Infinispan’s documentation for more
details.
If the Couchbase Java client and the couchbase-spring-cache
implementation are available and Couchbase is configured, a
CouchbaseCacheManager is auto-configured. It is also possible to create additional
caches on startup by setting the spring.cache.cache-names property. These caches
operate on the Bucket that was auto-configured. You can also create additional caches
on another Bucket by using the customizer. Assume you need two caches (cache1 and
cache2) on the "main" Bucket and one (cache3) cache with a custom time to live of 2
seconds on the “another” Bucket. You can create the first two caches through
configuration, as follows:
spring.cache.cache-names=cache1,cache2
Then you can define a @Configuration class to configure the extra Bucket and the
cache3 cache, as follows:
@Configuration(proxyBeanMethods = false)
public class CouchbaseCacheConfiguration {
    private final Cluster cluster;
    public CouchbaseCacheConfiguration(Cluster cluster) {
        this.cluster = cluster;
    @Bean
    public Bucket anotherBucket() {
        return this.cluster.openBucket("another", "secret");
    @Bean
    public CacheManagerCustomizer<CouchbaseCacheManager> cacheManagerCustomizer() {
        return c -> {
            c.prepareCache("cache3", CacheBuilder.newInstance(anotherBucket())
                    .withExpiration(2));
This sample configuration reuses the Cluster that was created through
auto-configuration.
12.1.7. Redis

If Redis is available and configured, a RedisCacheManager is
auto-configured. It is possible to create additional caches on startup by setting the
spring.cache.cache-names property and cache defaults can be configured by using
spring.cache.redis.* properties. For instance, the following configuration creates
cache1 and cache2 caches with a time to live of 10 minutes:
spring.cache.cache-names=cache1,cache2
spring.cache.redis.time-to-live=600000
By default, a key prefix is added so that, if two separate caches use the same
key, Redis does not have overlapping keys and cannot return invalid values. We strongly
recommend keeping this setting enabled if you create your own RedisCacheManager.
You can take full control of the configuration by adding a RedisCacheConfiguration
@Bean of your own. This can be useful if you’re looking for customizing the
serialization strategy.
Caffeine is a Java 8 rewrite of Guava’s cache that
supersedes support for Guava. If Caffeine is present, a CaffeineCacheManager (provided
by the spring-boot-starter-cache “Starter”) is auto-configured. Caches can be created
on startup by setting the spring.cache.cache-names property and can be customized by one
of the following (in the indicated order):
If a com.github.benmanes.caffeine.cache.CacheLoader bean is defined, it is
automatically associated to the CaffeineCacheManager. Since the CacheLoader is going
to be associated with all caches managed by the cache manager, it must be defined as
CacheLoader<Object, Object>. The auto-configuration ignores any other generic type.
12.1.9. Simple

If none of the other providers can be found, a simple implementation using a
ConcurrentHashMap as the cache store is configured. This is the default if no caching
library is present in your application. By default, caches are created as needed, but you
can restrict the list of available caches by setting the cache-names property. For
instance, if you want only cache1 and cache2 caches, set the cache-names property
as follows:
spring.cache.cache-names=cache1,cache2
If you do so and your application uses a cache not listed, then it fails at runtime when
the cache is needed, but not on startup. This is similar to the way the "real" cache
providers behave if you use an undeclared cache.
12.1.10. None

When @EnableCaching is present in your configuration, a suitable cache configuration is
expected as well. If you need to disable caching altogether in certain environments,
force the cache type to none to use a no-op implementation, as shown in the following
example:
spring.cache.type=none
The Spring Framework provides extensive support for integrating with messaging systems,
from simplified use of the JMS API using JmsTemplate to a complete infrastructure to
receive messages asynchronously. Spring AMQP provides a similar feature set for the
Advanced Message Queuing Protocol. Spring Boot also provides auto-configuration
options for RabbitTemplate and RabbitMQ. Spring WebSocket natively includes support for
STOMP messaging, and Spring Boot has support for that through starters and a small amount
of auto-configuration. Spring Boot also has support for Apache Kafka.
13.1. JMS

The javax.jms.ConnectionFactory interface provides a standard method of creating a
javax.jms.Connection for interacting with a JMS broker. Although Spring needs a
ConnectionFactory to work with JMS, you generally need not use it directly yourself and
can instead rely on higher level messaging abstractions. (See the
relevant section of the Spring Framework
reference documentation for details.) Spring Boot also auto-configures the necessary
infrastructure to send and receive messages.
13.1.1. ActiveMQ Support

When ActiveMQ is available on the classpath, Spring Boot can
also configure a ConnectionFactory. If the broker is present, an embedded broker is
automatically started and configured (provided no broker URL is specified through
configuration).
If you use spring-boot-starter-activemq, the necessary dependencies to connect or
embed an ActiveMQ instance are provided, as is the Spring infrastructure to integrate with
ActiveMQ configuration is controlled by external configuration properties in
spring.activemq.*. For example, you might declare the following section in
application.properties:
spring.activemq.broker-url=tcp://192.168.1.210:9876
spring.activemq.user=admin
spring.activemq.password=secret
By default, a CachingConnectionFactory wraps the native ConnectionFactory with
sensible settings that you can control by external configuration properties in
spring.jms.*:
spring.jms.cache.session-cache-size=5
If you’d rather use native pooling, you can do so by adding a dependency to
org.messaginghub:pooled-jms and configuring the JmsPoolConnectionFactory accordingly,
as shown in the following example:
spring.activemq.pool.enabled=true
spring.activemq.pool.max-connections=50
ActiveMQProperties
for more of the supported options. You can also register an arbitrary number of beans
that implement ActiveMQConnectionFactoryCustomizer for more advanced customizations.
13.1.2. Artemis Support

Spring Boot can auto-configure a ConnectionFactory when it detects that
Artemis is available on the classpath. If the broker
is present, an embedded broker is automatically started and configured (unless the mode
property has been explicitly set). The supported modes are embedded (to make explicit
that an embedded broker is required and that an error should occur if the broker is not
available on the classpath) and native (to connect to a broker using the netty
transport protocol). When the latter is configured, Spring Boot configures a
ConnectionFactory that connects to a broker running on the local machine with the
default settings.
If you use spring-boot-starter-artemis, the necessary dependencies to
connect to an existing Artemis instance are provided, as well as the Spring
infrastructure to integrate with JMS. Adding org.apache.activemq:artemis-jms-server to
your application lets you use embedded mode.
Artemis configuration is controlled by external configuration properties in
spring.artemis.*. For example, you might declare the following section in
application.properties:
spring.artemis.mode=native
spring.artemis.host=192.168.1.210
spring.artemis.port=9876
spring.artemis.user=admin
spring.artemis.password=secret
When embedding the broker, you can choose if you want to enable persistence and list the
destinations that should be made available. These can be specified as a comma-separated
list to create them with the default options, or you can define bean(s) of type
org.apache.activemq.artemis.jms.server.config.JMSQueueConfiguration or
org.apache.activemq.artemis.jms.server.config.TopicConfiguration, for advanced queue
and topic configurations, respectively.
By default, a CachingConnectionFactory wraps the native ConnectionFactory with
sensible settings that you can control by external configuration properties in
spring.jms.*:
spring.jms.cache.session-cache-size=5
If you’d rather use native pooling, you can do so by adding a dependency to
org.messaginghub:pooled-jms and configuring the JmsPoolConnectionFactory accordingly,
as shown in the following example:
spring.artemis.pool.enabled=true
spring.artemis.pool.max-connections=50
ArtemisProperties
for more supported options.
No JNDI lookup is involved, and destinations are resolved against their names, using
either the name attribute in the Artemis configuration or the names provided through
configuration.




    

13.1.3. Using a JNDI ConnectionFactory

If you are running your application in an application server, Spring Boot tries to
locate a JMS ConnectionFactory by using JNDI. By default, the java:/JmsXA and
java:/XAConnectionFactory location are checked. You can use the spring.jms.jndi-name
property if you need to specify an alternative location, as shown in the following
example:
spring.jms.jndi-name=java:/MyConnectionFactory
13.1.4. Sending a Message

Spring’s JmsTemplate is auto-configured, and you can autowire it directly into your own
beans, as shown in the following example:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jms.core.JmsTemplate;
import org.springframework.stereotype.Component;
@Component
public class MyBean {
    private final JmsTemplate jmsTemplate;
    @Autowired
    public MyBean(JmsTemplate jmsTemplate) {
        this.jmsTemplate = jmsTemplate;
    // ...
JmsMessagingTemplate can
be injected in a similar manner. If a DestinationResolver or a MessageConverter bean
is defined, it is associated automatically to the auto-configured JmsTemplate.
13.1.5. Receiving a Message

When the JMS infrastructure is present, any bean can be annotated with @JmsListener to
create a listener endpoint. If no JmsListenerContainerFactory has been defined, a
default one is configured automatically. If a DestinationResolver or a
MessageConverter beans is defined, it is associated automatically to the default
factory.
By default, the default factory is transactional. If you run in an infrastructure where a
JtaTransactionManager is present, it is associated to the listener container by default.
If not, the sessionTransacted flag is enabled. In that latter scenario, you can
associate your local data store transaction to the processing of an incoming message by
adding @Transactional on your listener method (or a delegate thereof). This ensures that
the incoming message is acknowledged, once the local transaction has completed. This also
includes sending response messages that have been performed on the same JMS session.
The following component creates a listener endpoint on the someQueue destination:
@Component
public class MyBean {
    @JmsListener(destination = "someQueue")
    public void processMessage(String content) {
        // ...
If you need to create more JmsListenerContainerFactory instances or if you want to
override the default, Spring Boot provides a
DefaultJmsListenerContainerFactoryConfigurer that you can use to initialize a
DefaultJmsListenerContainerFactory with the same settings as the one that is
auto-configured.
For instance, the following example exposes another factory that uses a specific
MessageConverter:
@Configuration(proxyBeanMethods = false)
static class JmsConfiguration {
    @Bean
    public DefaultJmsListenerContainerFactory myFactory(
            DefaultJmsListenerContainerFactoryConfigurer configurer) {
        DefaultJmsListenerContainerFactory factory =
                new DefaultJmsListenerContainerFactory();
        configurer.configure(factory, connectionFactory());
        factory.setMessageConverter(myMessageConverter());
        return factory;
Then you can use the factory in any @JmsListener-annotated method as follows:
@Component
public class MyBean {
    @JmsListener(destination = "someQueue", containerFactory="myFactory")
    public void processMessage(String content) {
        // ...
13.2. AMQP

The Advanced Message Queuing Protocol (AMQP) is a platform-neutral, wire-level protocol
for message-oriented middleware. The Spring AMQP project applies core Spring concepts to
the development of AMQP-based messaging solutions. Spring Boot offers several conveniences
for working with AMQP through RabbitMQ, including the spring-boot-starter-amqp
“Starter”.
13.2.1. RabbitMQ support

RabbitMQ is a lightweight, reliable, scalable, and portable
message broker based on the AMQP protocol. Spring uses RabbitMQ to communicate through
the AMQP protocol.
RabbitMQ configuration is controlled by external configuration properties in
spring.rabbitmq.*. For example, you might declare the following section in
application.properties:
spring.rabbitmq.host=localhost
spring.rabbitmq.port=5672
spring.rabbitmq.username=admin
spring.rabbitmq.password=secret
If a ConnectionNameStrategy bean exists in the context, it will be automatically used to
name connections created by the auto-configured ConnectionFactory. See
RabbitProperties for more
of the supported options.
13.2.2. Sending a Message

Spring’s AmqpTemplate and AmqpAdmin are auto-configured, and you can autowire them
directly into your own beans, as shown in the following example:
import org.springframework.amqp.core.AmqpAdmin;
import org.springframework.amqp.core.AmqpTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class MyBean {
    private final AmqpAdmin amqpAdmin;
    private final AmqpTemplate amqpTemplate;
    @Autowired
    public MyBean(AmqpAdmin amqpAdmin, AmqpTemplate amqpTemplate) {
        this.amqpAdmin = amqpAdmin;
        this.amqpTemplate = amqpTemplate;
    // ...
RabbitMessagingTemplate
can be injected in a similar manner. If a MessageConverter bean is defined, it is
associated automatically to the auto-configured AmqpTemplate.
If necessary, any org.springframework.amqp.core.Queue that is defined as a bean is
automatically used to declare a corresponding queue on the RabbitMQ instance.
To retry operations, you can enable retries on the AmqpTemplate (for example, in the
event that the broker connection is lost):
spring.rabbitmq.template.retry.enabled=true
spring.rabbitmq.template.retry.initial-interval=2s
Retries are disabled by default. You can also customize the RetryTemplate
programmatically by declaring a RabbitRetryTemplateCustomizer bean.
13.2.3. Receiving a Message

When the Rabbit infrastructure is present, any bean can be annotated with
@RabbitListener to create a listener endpoint. If no RabbitListenerContainerFactory
has been defined, a default SimpleRabbitListenerContainerFactory is automatically
configured and you can switch to a direct container using the
spring.rabbitmq.listener.type property.  If a MessageConverter or a MessageRecoverer
bean is defined, it is automatically associated with the default factory.
The following sample component creates a listener endpoint on the someQueue queue:
@Component
public class MyBean {
    @RabbitListener(queues = "someQueue")
    public void processMessage(String content) {
        // ...
If you need to create more RabbitListenerContainerFactory instances or if you want to
override the default, Spring Boot provides a
SimpleRabbitListenerContainerFactoryConfigurer and a
DirectRabbitListenerContainerFactoryConfigurer that you can use to initialize a
SimpleRabbitListenerContainerFactory and a DirectRabbitListenerContainerFactory with
the same settings as the factories used by the auto-configuration.
    @Bean
    public SimpleRabbitListenerContainerFactory myFactory(
            SimpleRabbitListenerContainerFactoryConfigurer configurer) {
        SimpleRabbitListenerContainerFactory factory =
                new SimpleRabbitListenerContainerFactory();
        configurer.configure(factory, connectionFactory);
        factory.setMessageConverter(myMessageConverter());
        return factory;
Then you can use the factory in any @RabbitListener-annotated method, as follows:
@Component
public class MyBean {
    @RabbitListener(queues = "someQueue", containerFactory="myFactory")
    public void processMessage(String content) {
        // ...
You can enable retries to handle situations where your listener throws an exception. By
default, RejectAndDontRequeueRecoverer is used, but you can define a MessageRecoverer
of your own. When retries are exhausted, the message is rejected and either dropped or
routed to a dead-letter exchange if the broker is configured to do so. By default,
retries are disabled. You can also customize the RetryTemplate programmatically by
declaring a RabbitRetryTemplateCustomizer bean.
By default, if retries are disabled and the listener throws an exception, the
delivery is retried indefinitely. You can modify this behavior in two ways: Set the
defaultRequeueRejected property to false so that zero re-deliveries are attempted or
throw an AmqpRejectAndDontRequeueException to signal the message should be rejected.
The latter is the mechanism used when retries are enabled and the maximum number of
delivery attempts is reached.
Kafka configuration is controlled by external configuration properties in
spring.kafka.*. For example, you might declare the following section in
application.properties:
spring.kafka.bootstrap-servers=localhost:9092
spring.kafka.consumer.group-id=myGroup
13.3.1. Sending a Message

Spring’s KafkaTemplate is auto-configured, and you can autowire it directly in your own
beans, as shown in the following example:
@Component
public class MyBean {
    private final KafkaTemplate kafkaTemplate;
    @Autowired
    public MyBean(KafkaTemplate kafkaTemplate) {
        this.kafkaTemplate = kafkaTemplate;
    // ...
If the property spring.kafka.producer.transaction-id-prefix is defined, a
KafkaTransactionManager is automatically configured. Also, if a RecordMessageConverter
bean is defined, it is automatically associated to the auto-configured KafkaTemplate.
13.3.2. Receiving a Message

When the Apache Kafka infrastructure is present, any bean can be annotated with
@KafkaListener to create a listener endpoint. If no KafkaListenerContainerFactory has
been defined, a default one is automatically configured with keys defined in
spring.kafka.listener.*.
The following component creates a listener endpoint on the someTopic topic:
@Component
public class MyBean {
    @KafkaListener(topics = "someTopic")
    public void processMessage(String content) {
        // ...
If a KafkaTransactionManager bean is defined, it is automatically associated to the
container factory. Similarly, if a ErrorHandler, AfterRollbackProcessor or
ConsumerAwareRebalanceListener bean is defined, it is automatically associated to the
default factory.
Depending on the listener type, a RecordMessageConverter or BatchMessageConverter bean
is associated to the default factory. If only a RecordMessageConverter bean is present
for a batch listener, it is wrapped in a BatchMessageConverter.
13.3.3. Kafka Streams

Spring for Apache Kafka provides a factory bean to create a StreamsBuilder object and
manage the lifecycle of its streams. Spring Boot auto-configures the required
KafkaStreamsConfiguration bean as long as kafka-streams is on the classpath and Kafka
Streams is enabled via the @EnableKafkaStreams annotation.
Enabling Kafka Streams means that the application id and bootstrap servers must be set.
The former can be configured using spring.kafka.streams.application-id, defaulting to
spring.application.name if not set. The latter can be set globally or
specifically overridden just for streams.
Several additional properties are available using dedicated properties; other arbitrary
Kafka properties can be set using the spring.kafka.streams.properties namespace. See
also Additional Kafka Properties for more information.
To use the factory bean, simply wire StreamsBuilder into your @Bean as shown in the
following example:
@Configuration(proxyBeanMethods = false)
@EnableKafkaStreams
public static class KafkaStreamsExampleConfiguration {
    @Bean
    public KStream<Integer, String> kStream(StreamsBuilder streamsBuilder) {
        KStream<Integer, String> stream = streamsBuilder.stream("ks1In");
        stream.map((k, v) -> new KeyValue<>(k, v.toUpperCase())).to("ks1Out",
                Produced.with(Serdes.Integer(), new JsonSerde<>()));
        return stream;
By default, the streams managed by the StreamBuilder object it creates are started
automatically. You can customize this behaviour using the
spring.kafka.streams.auto-startup property.
13.3.4. Additional Kafka Properties

The properties supported by auto configuration are shown in
[common-application-properties]. Note that, for the most part, these properties
(hyphenated or camelCase) map directly to the Apache Kafka dotted properties. Refer to the
Apache Kafka documentation for details.




    

The first few of these properties apply to all components (producers, consumers, admins,
and streams) but can be
specified at the component level if you wish to use different values.
Apache Kafka designates properties with an importance of HIGH, MEDIUM, or LOW. Spring Boot
auto-configuration supports all HIGH importance properties, some selected MEDIUM and LOW
properties, and any properties that do not have a default value.
Only a subset of the properties supported by Kafka are available directly through the
KafkaProperties class. If you wish to configure the producer or consumer with additional
properties that are not directly supported, use the following properties:
spring.kafka.properties.prop.one=first
spring.kafka.admin.properties.prop.two=second
spring.kafka.consumer.properties.prop.three=third
spring.kafka.producer.properties.prop.four=fourth
spring.kafka.streams.properties.prop.five=fifth
This sets the common prop.one Kafka property to first (applies to producers,
consumers and admins), the prop.two admin property to second, the prop.three
consumer property to third, the prop.four producer property to fourth and the
prop.five streams property to fifth.
You can also configure the Spring Kafka JsonDeserializer as follows:
spring.kafka.consumer.value-deserializer=org.springframework.kafka.support.serializer.JsonDeserializer
spring.kafka.consumer.properties.spring.json.value.default.type=com.example.Invoice
spring.kafka.consumer.properties.spring.json.trusted.packages=com.example,org.acme
Similarly, you can disable the JsonSerializer default behavior of sending type
information in headers:
spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer
spring.kafka.producer.properties.spring.json.add.type.headers=false
13.3.5. Testing with Embedded Kafka

Spring for Apache Kafka provides a convenient way to test projects with an embedded Apache Kafka
broker. To use this feature, annotate a test class with @EmbeddedKafka from the spring-kafka-test
module. For more information, please see the Spring for Apache Kafka
reference manual.
To make Spring Boot auto-configuration work with the aforementioned embedded Apache Kafka broker, you need
to remap a system property for embedded broker addresses (populated by the EmbeddedKafkaBroker)
into the Spring Boot configuration property for Apache Kafka. There are several ways to do that:
static {
    System.setProperty(EmbeddedKafkaBroker.BROKER_LIST_PROPERTY, "spring.kafka.bootstrap-servers");
If you need to call remote REST services from your application, you can use the Spring
Framework’s RestTemplate class. Since
RestTemplate instances often need to be customized before being used, Spring Boot does
not provide any single auto-configured RestTemplate bean. It does, however,
auto-configure a RestTemplateBuilder, which can be used to create RestTemplate
instances when needed. The auto-configured RestTemplateBuilder ensures that sensible
HttpMessageConverters are applied to RestTemplate instances.
The following code shows a typical example:
@Service
public class MyService {
    private final RestTemplate restTemplate;
    public MyService(RestTemplateBuilder restTemplateBuilder) {
        this.restTemplate = restTemplateBuilder.build();
    public Details someRestCall(String name) {
        return this.restTemplate.getForObject("/{name}/details", Details.class, name);
RestTemplateBuilder includes a number of useful methods that can be used to
quickly configure a RestTemplate. For example, to add BASIC auth support, you can use
builder.basicAuthentication("user", "password").build().
14.1. RestTemplate Customization

There are three main approaches to RestTemplate customization, depending on how broadly
you want the customizations to apply.
To make the scope of any customizations as narrow as possible, inject the auto-configured
RestTemplateBuilder and then call its methods as required. Each method call returns a
new RestTemplateBuilder instance, so the customizations only affect this use of the
builder.
To make an application-wide, additive customization, use a RestTemplateCustomizer bean.
All such beans are automatically registered with the auto-configured RestTemplateBuilder
and are applied to any templates that are built with it.
The following example shows a customizer that configures the use of a proxy for all hosts
except 192.168.0.5:
static class ProxyCustomizer implements RestTemplateCustomizer {
    @Override
    public void customize(RestTemplate restTemplate) {
        HttpHost proxy = new HttpHost("proxy.example.com");
        HttpClient httpClient = HttpClientBuilder.create().setRoutePlanner(new DefaultProxyRoutePlanner(proxy) {
            @Override
            public HttpHost determineProxy(HttpHost target, HttpRequest request, HttpContext context)
                    throws HttpException {
                if (target.getHostName().equals("192.168.0.5")) {
                    return null;
                return super.determineProxy(target, request, context);
        }).build();
        restTemplate.setRequestFactory(new HttpComponentsClientHttpRequestFactory(httpClient));
Finally, the most extreme (and rarely used) option is to create your own
RestTemplateBuilder bean. Doing so switches off the auto-configuration of a
RestTemplateBuilder and prevents any RestTemplateCustomizer beans from being used.
If you have Spring WebFlux on your classpath, you can also choose to use WebClient to
call remote REST services. Compared to RestTemplate, this client has a more functional
feel and is fully reactive. You can learn more about the WebClient in the dedicated
section in the Spring Framework docs.
Spring Boot creates and pre-configures a WebClient.Builder for you; it is strongly
advised to inject it in your components and use it to create WebClient instances.
Spring Boot is configuring that builder to share HTTP resources, reflect codecs
setup in the same fashion as the server ones (see
WebFlux HTTP codecs auto-configuration), and more.
The following code shows a typical example:
@Service
public class MyService {
    private final WebClient webClient;
    public MyService(WebClient.Builder webClientBuilder) {
        this.webClient = webClientBuilder.baseUrl("https://example.org").build();
    public Mono<Details> someRestCall(String name) {
        return this.webClient.get().uri("/{name}/details", name)
                        .retrieve().bodyToMono(Details.class);
15.1. WebClient Runtime

Spring Boot will auto-detect which ClientHttpConnector to use to drive WebClient,
depending on the libraries available on the application classpath. For now, Reactor
Netty and Jetty RS client are supported.
The spring-boot-starter-webflux starter depends on io.projectreactor.netty:reactor-netty
by default, which brings both server and client implementations. If you choose to use Jetty
as a reactive server instead, you should add a dependency on the Jetty Reactive HTTP
client library, org.eclipse.jetty:jetty-reactive-httpclient. Using the same technology
for server and client has it advantages, as it will automatically share HTTP resources
between client and server.
Developers can override the resource configuration for Jetty and Reactor Netty by providing
a custom ReactorResourceFactory or JettyResourceFactory bean - this will be applied to
both clients and servers.
If you wish to override that choice for the client, you can define your own
ClientHttpConnector bean and have full control over the client configuration.
You can learn more about the
WebClient configuration
options in the Spring Framework reference documentation.
15.2. WebClient Customization

There are three main approaches to WebClient customization, depending on how broadly you
want the customizations to apply.
To make the scope of any customizations as narrow as possible, inject the auto-configured
WebClient.Builder and then call its methods as required. WebClient.Builder instances
are stateful: Any change on the builder is reflected in all clients subsequently created
with it. If you want to create several clients with the same builder, you can also
consider cloning the builder with WebClient.Builder other = builder.clone();.
To make an application-wide, additive customization to all WebClient.Builder instances,
you can declare WebClientCustomizer beans and change the WebClient.Builder locally at
the point of injection.
Finally, you can fall back to the original API and use WebClient.create(). In that case,
no auto-configuration or WebClientCustomizer is applied.
The method validation feature supported by Bean Validation 1.1 is automatically enabled
as long as a JSR-303 implementation (such as Hibernate validator) is on the classpath.
This lets bean methods be annotated with javax.validation constraints on their
parameters and/or on their return value. Target classes with such annotated methods need
to be annotated with the @Validated annotation at the type level for their methods to
be searched for inline constraint annotations.
For instance, the following service triggers the validation of the first argument, making
sure its size is between 8 and 10:
@Service
@Validated
public class MyBean {
    public Archive findByCodeAndAuthor(@Size(min = 8, max = 10) String code,
            Author author) {
The Spring Framework provides an easy abstraction for sending email by using the
JavaMailSender interface, and Spring Boot provides auto-configuration for it as well as
a starter module.
If spring.mail.host and the relevant libraries (as defined by
spring-boot-starter-mail) are available, a default JavaMailSender is created if none
exists. The sender can be further customized by configuration items from the
spring.mail namespace. See
MailProperties for more
details.
In particular, certain default timeout values are infinite, and you may want to change
that to avoid having a thread blocked by an unresponsive mail server, as shown in the
following example:
spring.mail.properties.mail.smtp.connectiontimeout=5000
spring.mail.properties.mail.smtp.timeout=3000
spring.mail.properties.mail.smtp.writetimeout=5000
It is also possible to configure a JavaMailSender with an existing Session from JNDI:
spring.mail.jndi-name=mail/Session
When a jndi-name is set, it takes precedence over all other Session-related settings.
Spring Boot supports distributed JTA transactions across multiple XA resources by using
either an Atomikos or Bitronix
embedded transaction manager. JTA transactions are also supported when deploying to a
suitable Java EE Application Server.
When a JTA environment is detected, Spring’s JtaTransactionManager is used to manage
transactions. Auto-configured JMS, DataSource, and JPA beans are upgraded to support XA
transactions. You can use standard Spring idioms, such as @Transactional, to participate
in a distributed transaction. If you are within a JTA environment and still want to use
local transactions, you can set the spring.jta.enabled property to false to disable
the JTA auto-configuration.
18.1. Using an Atomikos Transaction Manager

Atomikos is a popular open source transaction manager which can
be embedded into your Spring Boot application. You can use the
spring-boot-starter-jta-atomikos Starter to pull in the appropriate Atomikos libraries.
Spring Boot auto-configures Atomikos and ensures that appropriate depends-on settings
are applied to your Spring beans for correct startup and shutdown ordering.
By default, Atomikos transaction logs are written to a transaction-logs directory in
your application’s home directory (the directory in which your application jar file
resides). You can customize the location of this directory by setting a
spring.jta.log-dir property in your application.properties file. Properties starting
with spring.jta.atomikos.properties can also be used to customize the Atomikos
UserTransactionServiceImp. See the
AtomikosProperties Javadoc
for complete details.
To ensure that multiple transaction managers can safely coordinate the same
resource managers, each Atomikos instance must be configured with a unique ID. By default,
this ID is the IP address of the machine on which Atomikos is running. To ensure
uniqueness in production, you should configure the spring.jta.transaction-manager-id
property with a different value for each instance of your application.
18.2. Using a Bitronix Transaction Manager

Bitronix is a popular open-source JTA transaction
manager implementation. You can use the spring-boot-starter-jta-bitronix starter to add
the appropriate Bitronix dependencies to your project. As with Atomikos, Spring Boot
automatically configures Bitronix and post-processes your beans to ensure that startup and
shutdown ordering is correct.
By default, Bitronix transaction log files (part1.btm and part2.btm) are written to
a transaction-logs directory in your application home directory. You can customize the
location of this directory by setting the spring.jta.log-dir property. Properties
starting with spring.jta.bitronix.properties are also bound to the
bitronix.tm.Configuration bean, allowing for complete customization. See the
Bitronix
documentation for details.




    

To ensure that multiple transaction managers can safely coordinate the same
resource managers, each Bitronix instance must be configured with a unique ID. By default,
this ID is the IP address of the machine on which Bitronix is running. To ensure
uniqueness in production, you should configure the spring.jta.transaction-manager-id
property with a different value for each instance of your application.
18.3. Using a Java EE Managed Transaction Manager

If you package your Spring Boot application as a war or ear file and deploy it to a
Java EE application server, you can use your application server’s built-in transaction
manager. Spring Boot tries to auto-configure a transaction manager by looking at common
JNDI locations (java:comp/UserTransaction, java:comp/TransactionManager, and so on).
If you use a transaction service provided by your application server, you generally also
want to ensure that all resources are managed by the server and exposed over JNDI. Spring
Boot tries to auto-configure JMS by looking for a ConnectionFactory at the JNDI path
(java:/JmsXA or java:/XAConnectionFactory), and you can use the
spring.datasource.jndi-name property
to configure your DataSource.
18.4. Mixing XA and Non-XA JMS Connections

When using JTA, the primary JMS ConnectionFactory bean is XA-aware and participates
in distributed transactions. In some situations, you might want to process certain JMS
messages by using a non-XA ConnectionFactory. For example, your JMS processing logic
might take longer than the XA timeout.
If you want to use a non-XA ConnectionFactory, you can inject the
nonXaJmsConnectionFactory bean rather than the @Primary jmsConnectionFactory bean.
For consistency, the jmsConnectionFactory bean is also provided by using the bean alias
xaJmsConnectionFactory.
The following example shows how to inject ConnectionFactory instances:
// Inject the primary (XA aware) ConnectionFactory
@Autowired
private ConnectionFactory defaultConnectionFactory;
// Inject the XA aware ConnectionFactory (uses the alias and injects the same as above)
@Autowired
@Qualifier("xaJmsConnectionFactory")
private ConnectionFactory xaConnectionFactory;
// Inject the non-XA aware ConnectionFactory
@Autowired
@Qualifier("nonXaJmsConnectionFactory")
private ConnectionFactory nonXaConnectionFactory;
18.5. Supporting an Alternative Embedded Transaction Manager

The XAConnectionFactoryWrapper
and XADataSourceWrapper interfaces
can be used to support alternative embedded transaction managers. The interfaces are
responsible for wrapping XAConnectionFactory and XADataSource beans and exposing them
as regular ConnectionFactory and DataSource beans, which transparently enroll in the
distributed transaction. DataSource and JMS auto-configuration use JTA variants, provided
you have a JtaTransactionManager bean and appropriate XA wrapper beans registered
within your ApplicationContext.
The BitronixXAConnectionFactoryWrapper
and BitronixXADataSourceWrapper
provide good examples of how to write XA wrappers.
If Hazelcast is on the classpath and a suitable configuration is
found, Spring Boot auto-configures a HazelcastInstance that you can inject in your
application.
If you define a com.hazelcast.config.Config bean, Spring Boot uses that. If your
configuration defines an instance name, Spring Boot tries to locate an existing instance
rather than creating a new one.
You could also specify the Hazelcast configuration file to use through configuration, as
shown in the following example:
spring.hazelcast.config=classpath:config/my-hazelcast.xml
Otherwise, Spring Boot tries to find the Hazelcast configuration from the default
locations: hazelcast.xml in the working directory or at the root of the classpath, or
a .yaml counterpart in the same locations. We also check if the hazelcast.config
system property is set. See the
Hazelcast documentation for
more details.
If hazelcast-client is present on the classpath, Spring Boot first attempts to create a
client by checking the following configuration options:
Spring Boot also has
explicit caching support for Hazelcast. If
caching is enabled, the HazelcastInstance is automatically wrapped in a CacheManager
implementation.
Spring Boot offers several conveniences for working with the
Quartz scheduler, including the
spring-boot-starter-quartz “Starter”. If Quartz is available, a Scheduler is
auto-configured (through the SchedulerFactoryBean abstraction).
Beans of the following types are automatically picked up and associated with the
Scheduler:
JobDetail: defines a particular Job. JobDetail instances can be built with the
JobBuilder API.
Calendar.
Trigger: defines when a particular job is triggered.
By default, an in-memory JobStore is used. However, it is possible to configure a
JDBC-based store if a DataSource bean is available in your application and if the
spring.quartz.job-store-type property is configured accordingly, as shown in the
following example:
spring.quartz.job-store-type=jdbc
When the JDBC store is used, the schema can be initialized on startup, as shown in the
following example:
spring.quartz.jdbc.initialize-schema=always
By default, the database is detected and initialized by using the standard scripts
provided with the Quartz library. These scripts drop existing tables, deleting all triggers
on every restart. It is also possible to provide a custom script by setting the
spring.quartz.jdbc.schema property.
To have Quartz use a DataSource other than the application’s main DataSource, declare
a DataSource bean, annotating its @Bean method with @QuartzDataSource. Doing so
ensures that the Quartz-specific DataSource is used by both the SchedulerFactoryBean
and for schema initialization.
By default, jobs created by configuration will not overwrite already registered jobs that
have been read from a persistent job store. To enable overwriting existing job definitions
set the spring.quartz.overwrite-existing-jobs property.
Quartz Scheduler configuration can be customized using spring.quartz properties and
SchedulerFactoryBeanCustomizer beans, which allow programmatic SchedulerFactoryBean
customization. Advanced Quartz configuration properties can be customized using
spring.quartz.properties.*.
In particular, an Executor bean is not associated with the scheduler as Quartz
offers a way to configure the scheduler via spring.quartz.properties. If you need
to customize the task executor, consider implementing SchedulerFactoryBeanCustomizer.
Jobs can define setters to inject data map properties. Regular beans can also be injected
in a similar manner, as shown in the following example:
public class SampleJob extends QuartzJobBean {
    private MyService myService;
    private String name;
    // Inject "MyService" bean
    public void setMyService(MyService myService) { ... }
    // Inject the "name" job data property
    public void setName(String name) { ... }
    @Override
    protected void executeInternal(JobExecutionContext context)
            throws JobExecutionException {
In the absence of an Executor bean in the context, Spring Boot auto-configures a
ThreadPoolTaskExecutor with sensible defaults that can be automatically associated to
asynchronous task execution (@EnableAsync) and Spring MVC asynchronous request
processing.
If you have defined a custom Executor in the context, regular task execution (i.e.
@EnableAsync) will use it transparently but the Spring MVC support will not be
configured as it requires an AsyncTaskExecutor implementation (named
applicationTaskExecutor). Depending on your target arrangement, you could change your
Executor into a ThreadPoolTaskExecutor or define both a ThreadPoolTaskExecutor and
an AsyncConfigurer wrapping your custom Executor.
The auto-configured TaskExecutorBuilder allows you to easily create instances that
reproduce what the auto-configuration does by default.
The thread pool uses 8 core threads that can grow and shrink according to the load. Those
default settings can be fine-tuned using the spring.task.execution namespace as shown in
the following example:
spring.task.execution.pool.max-threads=16
spring.task.execution.pool.queue-capacity=100
spring.task.execution.pool.keep-alive=10s
This changes the thread pool to use a bounded queue so that when the queue is full (100
tasks), the thread pool increases to maximum 16 threads. Shrinking of the pool is more
aggressive as threads are reclaimed when they are idle for 10 seconds (rather than
60 seconds by default).
A ThreadPoolTaskScheduler can also be auto-configured if need to be associated to
scheduled task execution (@EnableScheduling). The thread pool uses one thread by default
and those settings can be fine-tuned using the spring.task.scheduling namespace.
Both a TaskExecutorBuilder bean and a TaskSchedulerBuilder bean are made available in
the context if a custom executor or scheduler needs to be created.
Spring Boot offers several conveniences for working with Spring
Integration, including the spring-boot-starter-integration “Starter”. Spring
Integration provides abstractions over messaging and also other transports such as HTTP,
TCP, and others. If Spring Integration is available on your classpath, it is initialized
through the @EnableIntegration annotation.
Spring Boot also configures some features that are triggered by the presence of additional
Spring Integration modules. If spring-integration-jmx is also on the classpath,
message processing statistics are published over JMX . If spring-integration-jdbc is
available, the default database schema can be created on startup, as shown in the
following line:
spring.integration.jdbc.initialize-schema=always
See the
IntegrationAutoConfiguration
and IntegrationProperties
classes for more details.
By default, if a Micrometer meterRegistry bean is present, Spring Integration metrics
will be managed by Micrometer. If you wish to use legacy Spring Integration metrics, add
a DefaultMetricsFactory bean to the application context.
Spring Boot provides Spring Session auto-configuration for a wide range
of data stores. When building a Servlet web application, the following stores can be
auto-configured:
If a single Spring Session module is present on the classpath, Spring Boot uses that store
implementation automatically. If you have more than one implementation, you must choose
the StoreType that you wish
to use to store the sessions. For instance, to use JDBC as the back-end store, you can
configure your application as follows:
spring.session.store-type=jdbc
For setting the timeout of the session you can use the spring.session.timeout property.
If that property is not set, the auto-configuration falls back to the value of
server.servlet.session.timeout.
Java Management Extensions (JMX) provide a standard mechanism to monitor and manage
applications. Spring Boot exposes the most suitable MBeanServer as a bean with an ID of
mbeanServer. Any of your beans that are annotated with Spring JMX annotations (
@ManagedResource, @ManagedAttribute, or @ManagedOperation) are exposed to it.
If your platform provides a standard MBeanServer, Spring Boot will use that and default
to the VM MBeanServer if necessary. If all that fails, a new MBeanServer will be
created.
See the
JmxAutoConfiguration
class for more details.
Spring Boot provides a number of utilities and annotations to help when testing your
application. Test support is provided by two modules: spring-boot-test contains core
items, and spring-boot-test-autoconfigure supports auto-configuration for tests.
Most developers use the spring-boot-starter-test “Starter”, which imports both Spring
Boot test modules as well as JUnit Jupiter, AssertJ, Hamcrest, and a number of other
useful libraries.
The starter also brings the vintage engine so that you can run both JUnit 4 and JUnit 5
tests. If you have migrated your tests to JUnit 5, you should exclude JUnit 4 support, as
shown in the following example:
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <scope>test</scope>
    <exclusions>
        <exclusion>
            <groupId>org.junit.vintage</groupId>
            <artifactId>junit-vintage-engine</artifactId>
        </exclusion>
    </exclusions>
</dependency>
25.1. Test Scope Dependencies

The spring-boot-starter-test “Starter” (in the test scope) contains
the following provided libraries:
JUnit 5 (including the vintage engine for backward
compatibility with JUnit 4: The de-facto standard for unit testing Java applications.
Spring Test & Spring Boot Test:
Utilities and integration test support for Spring Boot applications.
AssertJ: A fluent assertion library.
Hamcrest: A library of matcher objects (also
known as constraints or predicates).
Mockito: A Java mocking framework.
JSONassert: An assertion library for JSON.




    

JsonPath: XPath for JSON.
25.2. Testing Spring Applications

One of the major advantages of dependency injection is that it should make your code
easier to unit test. You can instantiate objects by using the new operator without
even involving Spring. You can also use mock objects instead of real dependencies.
Often, you need to move beyond unit testing and start integration testing (with
a Spring ApplicationContext). It is useful to be able to perform integration testing
without requiring deployment of your application or needing to connect to other
infrastructure.
The Spring Framework includes a dedicated test module for such integration testing. You
can declare a dependency directly to org.springframework:spring-test or use the
spring-boot-starter-test “Starter” to pull it in transitively.
If you have not used the spring-test module before, you should start by reading the
relevant section of the Spring Framework
reference documentation.
25.3. Testing Spring Boot Applications

A Spring Boot application is a Spring ApplicationContext, so nothing very special has
to be done to test it beyond what you would normally do with a vanilla Spring context.
Spring Boot provides a @SpringBootTest annotation, which can be used as an alternative
to the standard spring-test @ContextConfiguration annotation when you need Spring
Boot features. The annotation works by
creating the
ApplicationContext used in your tests through SpringApplication. In addition to
@SpringBootTest a number of other annotations are also provided for
testing more
specific slices of an application.
If you are using JUnit 4, don’t forget to also add @RunWith(SpringRunner.class) to
your test, otherwise the annotations will be ignored. If you are using JUnit 5, there’s no
need to add the equivalent @RunWith(SpringExtension.class) as @SpringBootTest and
the other @…Test annotations are already annotated with it.
MOCK(Default) : Loads a web ApplicationContext and provides a mock web
environment. Embedded servers are not started when using this annotation. If a web
environment is not available on your classpath, this mode transparently falls back to
creating a regular non-web ApplicationContext. It can be used in conjunction with
@AutoConfigureMockMvc or @AutoConfigureWebTestClient for mock-based testing of your
web application.
RANDOM_PORT: Loads a WebServerApplicationContext and provides a real web
environment. Embedded servers are started and listen on a random port.
DEFINED_PORT: Loads a WebServerApplicationContext and provides a real web
environment. Embedded servers are started and listen on a defined port (from your
application.properties) or on the default port of 8080.
NONE: Loads an ApplicationContext by using SpringApplication but does not provide
any web environment (mock or otherwise).
If your test is @Transactional, it rolls back the transaction at the end of each
test method by default. However, as using this arrangement with either RANDOM_PORT or
DEFINED_PORT implicitly provides a real servlet environment, the HTTP client and server
run in separate threads and, thus, in separate transactions. Any transaction initiated on
the server does not roll back in this case.
@SpringBootTest with webEnvironment = WebEnvironment.RANDOM_PORT will also
start the management server on a separate random port if your application uses a different
port for the management server.
25.3.1. Detecting Web Application Type

If Spring MVC is available, a regular MVC-based application context is configured. If you
have only Spring WebFlux, we’ll detect that and configure a WebFlux-based application
context instead.
If both are present, Spring MVC takes precedence. If you want to test a reactive web
application in this scenario, you must set the spring.main.web-application-type
property:
@SpringBootTest(properties = "spring.main.web-application-type=reactive")
class MyWebFluxTests { ... }
25.3.2. Detecting Test Configuration

If you are familiar with the Spring Test Framework, you may be used to using
@ContextConfiguration(classes=…) in order to specify which Spring @Configuration to
load. Alternatively, you might have often used nested @Configuration classes within
your test.
When testing Spring Boot applications, this is often not required. Spring Boot’s @*Test
annotations search for your primary configuration automatically whenever you do not
explicitly define one.
The search algorithm works up from the package that contains the test until it finds a
class annotated with @SpringBootApplication or @SpringBootConfiguration. As long as
you structured your code in a sensible way, your
main configuration is usually found.
If you use a
annotation to test a more specific slice of your application, you should avoid adding
configuration settings that are specific to a particular area on the
method’s application class.
The underlying component scan configuration of @SpringBootApplication defines exclude
filters that are used to make sure slicing works as expected. If you are using an explicit
@ComponentScan directive on your @SpringBootApplication-annotated class, be aware that
those filters will be disabled. If you are using slicing, you should define them again.
If you want to customize the primary configuration, you can use a nested
@TestConfiguration class. Unlike a nested @Configuration class, which would be used
instead of your application’s primary configuration, a nested @TestConfiguration class
is used in addition to your application’s primary configuration.
Spring’s test framework caches application contexts between tests. Therefore, as
long as your tests share the same configuration (no matter how it is discovered), the
potentially time-consuming process of loading the context happens only once.
25.3.3. Excluding Test Configuration

If your application uses component scanning (for example, if you use
@SpringBootApplication or @ComponentScan), you may find top-level configuration
classes that you created only for specific tests accidentally get picked up everywhere.
As we have seen
earlier, @TestConfiguration can be used on an inner class of a test to customize the
primary configuration. When placed on a top-level class, @TestConfiguration indicates
that classes in src/test/java should not be picked up by scanning. You can then import
that class explicitly where it is required, as shown in the following example:
@SpringBootTest
@Import(MyTestsConfiguration.class)
class MyTests {
    @Test
    void exampleTest() {
If you directly use @ComponentScan (that is, not through
@SpringBootApplication) you need to register the TypeExcludeFilter with it. See
the Javadoc for details.
    @Test
    void applicationArgumentsPopulated(@Autowired ApplicationArguments args) {
        assertThat(args.getOptionNames()).containsOnly("app.test");
        assertThat(args.getOptionValues("app.test")).containsOnly("one");
25.3.5. Testing with a mock environment

By default, @SpringBootTest does not start the server. If you have web endpoints that
you want to test against this mock environment, you can additionally configure
MockMvc as shown in the
following example:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.servlet.MockMvc;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
@SpringBootTest
@AutoConfigureMockMvc
class MockMvcExampleTests {
    @Test
    void exampleTest(@Autowired MockMvc mvc) throws Exception {
        mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
If you want to focus only on the web layer and not start a complete
ApplicationContext, consider
using
@WebMvcTest instead.
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.AutoConfigureWebTestClient;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.web.reactive.server.WebTestClient;
@SpringBootTest
@AutoConfigureWebTestClient
class MockWebTestClientExampleTests {
    @Test
    void exampleTest(@Autowired WebTestClient webClient) {
        webClient.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class).isEqualTo("Hello World");
25.3.6. Testing with a running server

If you need to start a full running server, we recommend that you use random ports.
If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT), an
available port is picked at random each time your test runs.
The @LocalServerPort annotation can be used to
inject the actual port used into your test.
For convenience, tests that need to make REST calls to the started server can
additionally @Autowire a
WebTestClient, which resolves
relative links to the running server and comes with a dedicated API for verifying
responses, as shown in the following example:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.test.web.reactive.server.WebTestClient;
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class RandomPortWebTestClientExampleTests {
    @Test
    void exampleTest(@Autowired WebTestClient webClient) {
        webClient.get().uri("/").exchange().expectStatus().isOk().expectBody(String.class).isEqualTo("Hello World");
This setup requires spring-webflux on the classpath. If you can’t or won’t add webflux,
Spring Boot also provides a TestRestTemplate facility:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.web.client.TestRestTemplate;
import static org.assertj.core.api.Assertions.assertThat;
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class RandomPortTestRestTemplateExampleTests {
    @Test
    void exampleTest(@Autowired TestRestTemplate restTemplate) {
        String body = restTemplate.getForObject("/", String.class);
        assertThat(body).isEqualTo("Hello World");
25.3.7. Using JMX

As the test context framework caches context, JMX is disabled by default to prevent
identical components to register on the same domain. If such test needs access to an
MBeanServer, consider marking it dirty as well:
@ExtendWith(SpringExtension.class)
@SpringBootTest(properties = "spring.jmx.enabled=true")
@DirtiesContext
class SampleJmxTests {
    @Autowired
    private MBeanServer mBeanServer;
    @Test
    void exampleTest() {
        // ...
25.3.8. Mocking and Spying Beans

When running tests, it is sometimes necessary to mock certain components within your
application context. For example, you may have a facade over some remote service that is
unavailable during development. Mocking can also be useful when you want to simulate
failures that might be hard to trigger in a real environment.
Spring Boot includes a @MockBean annotation that can be used to define a Mockito mock
for a bean inside your ApplicationContext. You can use the annotation to add new beans
or replace a single existing bean definition. The annotation can be used directly on test
classes, on fields within your test, or on @Configuration classes and fields. When used
on a field, the instance of the created mock is also injected. Mock beans are
automatically reset after each test method.
If your test uses one of Spring Boot’s test annotations (such as @SpringBootTest), this
feature is automatically enabled. To use this feature with a different
arrangement, a listener must be explicitly added, as shown in the following example:
@TestExecutionListeners(MockitoTestExecutionListener.class)
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.context.*;
import org.springframework.boot.test.mock.mockito.*;
import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;
@SpringBootTest
class MyTests {
    @MockBean
    private RemoteService remoteService;
    @Autowired
    private Reverser reverser;
    @Test
    void exampleTest() {
        // RemoteService has been injected into the reverser bean
        given(this.remoteService.someCall()).willReturn("mock");
        String reverse = reverser.reverseSomeCall();
        assertThat(reverse).isEqualTo("kcom");
@MockBean cannot be used to mock the behavior of a bean that’s exercised during
application context refresh. By the time the test is executed, the application context refresh
has completed and it is too late to configure the mocked behavior. We recommend using a @Bean
method to create and configure the mock in this situation.
While Spring’s test framework caches application contexts between tests and reuses
a context for tests sharing the same configuration, the use of @MockBean or @SpyBean
influences the cache key, which will most likely increase the number of contexts.
If you are using @SpyBean to spy on a bean with @Cacheable methods that refer
to parameters by name, your application must be compiled with -parameters. This
ensures that the parameter names are available to the caching infrastructure once the
bean has been spied upon.
25.3.9. Auto-configured Tests

Spring Boot’s auto-configuration system works well for applications but can sometimes be
a little too much for tests. It often helps to load only the parts of the configuration
that are required to test a “slice” of your application. For example, you might want to
test that Spring MVC controllers are mapping URLs correctly, and you do not want to
involve database calls in those tests, or you might want to test JPA entities, and you
are not interested in the web layer when those tests run.




    

The spring-boot-test-autoconfigure module includes a number of annotations that can be
used to automatically configure such “slices”. Each of them works in a similar way,
providing a @…Test annotation that loads the ApplicationContext and one or
more @AutoConfigure… annotations that can be used to customize auto-configuration
settings.
Each slice restricts component scan to appropriate components and loads a very
restricted set of auto-configuration classes. If you need to exclude one of them,
most @…Test annotations provide an excludeAutoConfiguration attribute.
Alternatively, you can use @ImportAutoConfiguration#exclude.
Including multiple “slices” by using several @…Test annotations in one test is
not supported. If you need multiple “slices”, pick one of the @…Test annotations
and include the @AutoConfigure… annotations of the other “slices” by hand.
It is also possible to use the @AutoConfigure… annotations with the standard
@SpringBootTest annotation. You can use this combination if you are not interested in
“slicing” your application but you want some of the auto-configured test beans.
25.3.10. Auto-configured JSON Tests

To test that object JSON serialization and deserialization is working as expected, you can
use the @JsonTest annotation. @JsonTest auto-configures the available supported JSON
mapper, which can be one of the following libraries:
If you need to configure elements of the auto-configuration, you can use the
@AutoConfigureJsonTesters annotation.
Spring Boot includes AssertJ-based helpers that work with the JSONAssert and JsonPath
libraries to check that JSON appears as expected. The JacksonTester, GsonTester,
JsonbTester, and BasicJsonTester classes can be used for Jackson, Gson, Jsonb, and
Strings respectively. Any helper fields on the test class can be @Autowired when using
@JsonTest. The following example shows a test class for Jackson:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.json.*;
import org.springframework.boot.test.context.*;
import org.springframework.boot.test.json.*;
import static org.assertj.core.api.Assertions.*;
@JsonTest
class MyJsonTests {
    @Autowired
    private JacksonTester<VehicleDetails> json;
    @Test
    void testSerialize() throws Exception {
        VehicleDetails details = new VehicleDetails("Honda", "Civic");
        // Assert against a `.json` file in the same package as the test
        assertThat(this.json.write(details)).isEqualToJson("expected.json");
        // Or use JSON path based assertions
        assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
        assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make")
                .isEqualTo("Honda");
    @Test
    void testDeserialize() throws Exception {
        String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
        assertThat(this.json.parse(content))
                .isEqualTo(new VehicleDetails("Ford", "Focus"));
        assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
JSON helper classes can also be used directly in standard unit tests. To do so,
call the initFields method of the helper in your @Before method if you do not use
@JsonTest.
If you’re using Spring Boot’s AssertJ-based helpers to assert on a number value
at a given JSON path, you might not be able to use isEqualTo depending on the type.
Instead, you can use AssertJ’s satisfies to assert that the value matches the given
condition. For instance, the following example asserts that the actual number is a float
value close to 0.15 within an offset of 0.01.
assertThat(json.write(message))
    .extractingJsonPathNumberValue("@.test.numberValue")
    .satisfies((number) -> assertThat(number.floatValue()).isCloseTo(0.15f, within(0.01f)));
25.3.11. Auto-configured Spring MVC Tests

To test whether Spring MVC controllers are working as expected, use the @WebMvcTest
annotation. @WebMvcTest auto-configures the Spring MVC infrastructure and limits
scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter,
GenericConverter, Filter, HandlerInterceptor, WebMvcConfigurer, and
HandlerMethodArgumentResolver. Regular @Component beans are not scanned when using
this annotation.
Often, @WebMvcTest is limited to a single controller and is used in combination with
@MockBean to provide mock implementations for required collaborators.
@WebMvcTest also auto-configures MockMvc. Mock MVC offers a powerful way to quickly
test MVC controllers without needing to start a full HTTP server.
You can also auto-configure MockMvc in a non-@WebMvcTest (such as
@SpringBootTest) by annotating it with @AutoConfigureMockMvc. The following example
uses MockMvc:
import org.junit.jupiter.api.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.web.servlet.*;
import org.springframework.boot.test.mock.mockito.*;
import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
@WebMvcTest(UserVehicleController.class)
class MyControllerTests {
    @Autowired
    private MockMvc mvc;
    @MockBean
    private UserVehicleService userVehicleService;
    @Test
    void testExample() throws Exception {
        given(this.userVehicleService.getVehicleDetails("sboot"))
                .willReturn(new VehicleDetails("Honda", "Civic"));
        this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
                .andExpect(status().isOk()).andExpect(content().string("Honda Civic"));
If you need to configure elements of the auto-configuration (for example, when
servlet filters should be applied) you can use attributes in the @AutoConfigureMockMvc
annotation.
import com.gargoylesoftware.htmlunit.*;
import org.junit.jupiter.api.*;
import org.springframework.beans.factory.annotation.*;
import org.springframework.boot.test.autoconfigure.web.servlet.*;
import org.springframework.boot.test.mock.mockito.*;
import static org.assertj.core.api.Assertions.*;
import static org.mockito.BDDMockito.*;
@WebMvcTest(UserVehicleController.class)
class MyHtmlUnitTests {
    @Autowired
    private WebClient webClient;
    @MockBean
    private UserVehicleService userVehicleService;
    @Test
    void testExample() throws Exception {
        given(this.userVehicleService.getVehicleDetails("sboot"))
                .willReturn(new VehicleDetails("Honda", "Civic"));
        HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
        assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
By default, Spring Boot puts WebDriver beans in a special “scope” to ensure
that the driver exits after each test and that a new instance is injected. If you do
not want this behavior, you can add @Scope("singleton") to your WebDriver @Bean
definition.
The webDriver scope created by Spring Boot will replace any user defined scope
of the same name. If you define your own webDriver scope you may find it stops working
when you use @WebMvcTest.
If you have Spring Security on the classpath, @WebMvcTest will also scan WebSecurityConfigurer
beans. Instead of disabling security completely for such tests, you can use Spring Security’s test support.
More details on how to use Spring Security’s MockMvc support can be found in
this howto.html how-to section.

To test that Spring WebFlux controllers are
working as expected, you can use the @WebFluxTest annotation. @WebFluxTest
auto-configures the Spring WebFlux infrastructure and limits scanned beans to
@Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter,
WebFilter, and WebFluxConfigurer. Regular @Component beans are not scanned when the
@WebFluxTest annotation is used.
Often, @WebFluxTest is limited to a single controller and used in combination with the
@MockBean annotation to provide mock implementations for required collaborators.
@WebFluxTest also auto-configures
WebTestClient, which offers
a powerful way to quickly test WebFlux controllers without needing to start a full HTTP
server.
You can also auto-configure WebTestClient in a non-@WebFluxTest (such as
@SpringBootTest) by annotating it with @AutoConfigureWebTestClient. The following
example shows a class that uses both @WebFluxTest and a WebTestClient:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.reactive.server.WebTestClient;
@WebFluxTest(UserVehicleController.class)
class MyControllerTests {
    @Autowired
    private WebTestClient webClient;
    @MockBean
    private UserVehicleService userVehicleService;
    @Test
    void testExample() throws Exception {
        given(this.userVehicleService.getVehicleDetails("sboot"))
                .willReturn(new VehicleDetails("Honda", "Civic"));
        this.webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN)
                .exchange()
                .expectStatus().isOk()
                .expectBody(String.class).isEqualTo("Honda Civic");
@WebFluxTest cannot detect routes registered via the functional web framework. For
testing RouterFunction beans in the context, consider importing your RouterFunction
yourself via @Import or using @SpringBootTest.
@WebFluxTest cannot detect custom security configuration registered via a @Bean
of type SecurityWebFilterChain. To include that in your test, you will need to import
the configuration that registers the bean via @Import or use @SpringBootTest.
25.3.13. Auto-configured Data JPA Tests

You can use the @DataJpaTest annotation to test JPA applications. By default, it scans
for @Entity classes and configures Spring Data JPA repositories. If an embedded database
is available on the classpath, it configures one as well. Regular @Component beans are
not loaded into the ApplicationContext.
By default, data JPA tests are transactional and roll back at the end of each test. See
the relevant section
in the Spring Framework Reference Documentation for more details. If that is not what you
want, you can disable transaction management for a test or for the whole class as
follows:
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class ExampleNonTransactionalTests {
Data JPA tests may also inject a
TestEntityManager
bean, which provides an alternative to the standard JPA EntityManager that is
specifically designed for tests. If you want to use TestEntityManager outside of
@DataJpaTest instances, you can also use the @AutoConfigureTestEntityManager
annotation. A JdbcTemplate is also available if you need that. The following example
shows the @DataJpaTest annotation in use:
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.autoconfigure.orm.jpa.*;
import static org.assertj.core.api.Assertions.*;
@DataJpaTest
class ExampleRepositoryTests {
    @Autowired
    private TestEntityManager entityManager;
    @Autowired
    private UserRepository repository;
    @Test
    void testExample() throws Exception {
        this.entityManager.persist(new User("sboot", "1234"));
        User user = this.repository.findByUsername("sboot");
        assertThat(user.getUsername()).isEqualTo("sboot");
        assertThat(user.getVin()).isEqualTo("1234");
In-memory embedded databases generally work well for tests, since they are fast and do
not require any installation. If, however, you prefer to run tests against a real
database you can use the @AutoConfigureTestDatabase annotation, as shown in the
following example:




    

@DataJpaTest
@AutoConfigureTestDatabase(replace=Replace.NONE)
class ExampleRepositoryTests {
    // ...
25.3.14. Auto-configured JDBC Tests

@JdbcTest is similar to @DataJpaTest but is for tests that only require a
DataSource and do not use Spring Data JDBC. By default, it configures an in-memory
embedded database and a JdbcTemplate. Regular @Component beans are not loaded into
the ApplicationContext.
By default, JDBC tests are transactional and roll back at the end of each test. See the
relevant section in
the Spring Framework Reference Documentation for more details. If that is not what you
want, you can disable transaction management for a test or for the whole class, as
follows:
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.autoconfigure.jdbc.JdbcTest;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class ExampleNonTransactionalTests {
If you prefer your test to run against a real database, you can use the
@AutoConfigureTestDatabase annotation in the same way as for DataJpaTest. (See
"Auto-configured Data JPA Tests".)
25.3.15. Auto-configured Data JDBC Tests

@DataJdbcTest is similar to @JdbcTest but is for tests that use Spring Data JDBC
repositories. By default, it configures an in-memory embedded database, a JdbcTemplate,
and Spring Data JDBC repositories. Regular @Component beans are not loaded into
the ApplicationContext.
By default, Data JDBC tests are transactional and roll back at the end of each test. See
the relevant section
in the Spring Framework Reference Documentation for more details. If that is not what you
want, you can disable transaction management for a test or for the whole test class as
shown
in the JDBC example.
If you prefer your test to run against a real database, you can use the
@AutoConfigureTestDatabase annotation in the same way as for DataJpaTest. (See
"Auto-configured Data JPA Tests".)
25.3.16. Auto-configured jOOQ Tests

You can use @JooqTest in a similar fashion as @JdbcTest but for jOOQ-related tests.
As jOOQ relies heavily on a Java-based schema that corresponds with the database schema,
the existing DataSource is used. If you want to replace it with an in-memory database,
you can use @AutoConfigureTestDatabase to override those settings. (For more about using
jOOQ with Spring Boot, see "Using jOOQ", earlier in this chapter.) Regular
@Component beans are not loaded into the ApplicationContext.
import org.jooq.DSLContext;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.autoconfigure.jooq.JooqTest;
@JooqTest
class ExampleJooqTests {
    @Autowired
    private DSLContext dslContext;
JOOQ tests are transactional and roll back at the end of each test by default. If that is
not what you want, you can disable transaction management for a test or for the whole
test class as
shown
in the JDBC example.
25.3.17. Auto-configured Data MongoDB Tests

You can use @DataMongoTest to test MongoDB applications. By default, it configures an
in-memory embedded MongoDB (if available), configures a MongoTemplate, scans for
@Document classes, and configures Spring Data MongoDB repositories. Regular
@Component beans are not loaded into the ApplicationContext. (For more about using
MongoDB with Spring Boot, see "MongoDB", earlier in this chapter.)
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
import org.springframework.data.mongodb.core.MongoTemplate;
@DataMongoTest
class ExampleDataMongoTests {
    @Autowired
    private MongoTemplate mongoTemplate;
In-memory embedded MongoDB generally works well for tests, since it is fast and does not
require any developer installation. If, however, you prefer to run tests against a real
MongoDB server, you should exclude the embedded MongoDB auto-configuration, as shown in
the following example:
import org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
@DataMongoTest(excludeAutoConfiguration = EmbeddedMongoAutoConfiguration.class)
class ExampleDataMongoNonEmbeddedTests {
25.3.18. Auto-configured Data Neo4j Tests

You can use @DataNeo4jTest to test Neo4j applications. By default, it uses an in-memory
embedded Neo4j (if the embedded driver is available), scans for @NodeEntity classes, and
configures Spring Data Neo4j repositories. Regular @Component beans are not loaded into
the ApplicationContext. (For more about using Neo4J with Spring Boot, see
"Neo4j", earlier in this chapter.)
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
@DataNeo4jTest
class ExampleDataNeo4jTests {
    @Autowired
    private YourRepository repository;
By default, Data Neo4j tests are transactional and roll back at the end of each test.
See the relevant
section in the Spring Framework Reference Documentation for more details. If that is not
what you want, you can disable transaction management for a test or for the whole class,
as follows:
import org.springframework.boot.test.autoconfigure.data.neo4j.DataNeo4jTest;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class ExampleNonTransactionalTests {
25.3.19. Auto-configured Data Redis Tests

You can use @DataRedisTest to test Redis applications. By default, it scans for
@RedisHash classes and configures Spring Data Redis repositories. Regular @Component
beans are not loaded into the ApplicationContext. (For more about using Redis with
Spring Boot, see "Redis", earlier in this chapter.)
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.redis.DataRedisTest;
@DataRedisTest
class ExampleDataRedisTests {
    @Autowired
    private YourRepository repository;
25.3.20. Auto-configured Data LDAP Tests

You can use @DataLdapTest to test LDAP applications. By default, it configures an
in-memory embedded LDAP (if available), configures an LdapTemplate, scans for @Entry
classes, and configures Spring Data LDAP repositories. Regular @Component beans are not
loaded into the ApplicationContext. (For more about using LDAP with
Spring Boot, see "LDAP", earlier in this chapter.)
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
import org.springframework.ldap.core.LdapTemplate;
@DataLdapTest
class ExampleDataLdapTests {
    @Autowired
    private LdapTemplate ldapTemplate;
In-memory embedded LDAP generally works well for tests, since it is fast and does not
require any developer installation. If, however, you prefer to run tests against a real
LDAP server, you should exclude the embedded LDAP auto-configuration, as shown in the
following example:
import org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration;
import org.springframework.boot.test.autoconfigure.data.ldap.DataLdapTest;
@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
class ExampleDataLdapNonEmbeddedTests {
25.3.21. Auto-configured REST Clients

You can use the @RestClientTest annotation to test REST clients. By default, it
auto-configures Jackson, GSON, and Jsonb support, configures a RestTemplateBuilder, and
adds support for MockRestServiceServer. Regular @Component beans are not loaded into
the ApplicationContext.
    void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails()
            throws Exception {
        this.server.expect(requestTo("/greet/details"))
                .andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
        String greeting = this.service.callRestService();
        assertThat(greeting).isEqualTo("hello");
25.3.22. Auto-configured Spring REST Docs Tests

You can use the @AutoConfigureRestDocs annotation to use Spring REST
Docs in your tests with Mock MVC, REST Assured, or WebTestClient. It removes the need for
the JUnit extension in Spring REST Docs.
@AutoConfigureRestDocs can be used to override the default output directory
(target/generated-snippets if you are using Maven or build/generated-snippets if you
are using Gradle). It can also be used to configure the host, scheme, and port that
appears in any documented URIs.
Auto-configured Spring REST Docs Tests with Mock MVC

@AutoConfigureRestDocs customizes the MockMvc bean to use Spring REST Docs. You can
inject it by using @Autowired and use it in your tests as you normally would when using
Mock MVC and Spring REST Docs, as shown in the following example:
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import org.springframework.http.MediaType;
import org.springframework.test.web.servlet.MockMvc;
import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
@WebMvcTest(UserController.class)
@AutoConfigureRestDocs
class UserDocumentationTests {
    @Autowired
    private MockMvc mvc;
    @Test
    void listUsers() throws Exception {
        this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
                .andExpect(status().isOk())
                .andDo(document("list-users"));
If you require more control over Spring REST Docs configuration than offered by the
attributes of @AutoConfigureRestDocs, you can use a
RestDocsMockMvcConfigurationCustomizer bean, as shown in the following example:
@TestConfiguration
static class CustomizationConfiguration
        implements RestDocsMockMvcConfigurationCustomizer {
    @Override
    public void customize(MockMvcRestDocumentationConfigurer configurer) {
        configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
If you want to make use of Spring REST Docs support for a parameterized output directory,
you can create a RestDocumentationResultHandler bean. The auto-configuration calls
alwaysDo with this result handler, thereby causing each MockMvc call to automatically
generate the default snippets. The following example shows a
RestDocumentationResultHandler being defined:
@TestConfiguration
static class ResultHandlerConfiguration {
    @Bean
    public RestDocumentationResultHandler restDocumentation() {
        return MockMvcRestDocumentation.document("{method-name}");
Auto-configured Spring REST Docs Tests with WebTestClient

@AutoConfigureRestDocs can also be used with WebTestClient. You can inject it by using
@Autowired and use it in your tests as you normally would when using @WebFluxTest and
Spring REST Docs, as shown in the following example:




    

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.autoconfigure.web.reactive.WebFluxTest;
import org.springframework.test.web.reactive.server.WebTestClient;
import static org.springframework.restdocs.webtestclient.WebTestClientRestDocumentation.document;
@WebFluxTest
@AutoConfigureRestDocs
class UsersDocumentationTests {
    @Autowired
    private WebTestClient webTestClient;
    @Test
    void listUsers() {
        this.webTestClient.get().uri("/").exchange().expectStatus().isOk().expectBody()
                .consumeWith(document("list-users"));
If you require more control over Spring REST Docs configuration than offered by the
attributes of @AutoConfigureRestDocs, you can use a
RestDocsWebTestClientConfigurationCustomizer bean, as shown in the following example:
@TestConfiguration
public static class CustomizationConfiguration implements RestDocsWebTestClientConfigurationCustomizer {
    @Override
    public void customize(WebTestClientRestDocumentationConfigurer configurer) {
        configurer.snippets().withEncoding("UTF-8");
Auto-configured Spring REST Docs Tests with REST Assured

@AutoConfigureRestDocs makes a RequestSpecification bean, preconfigured to use Spring
REST Docs, available to your tests. You can inject it by using @Autowired and use it in
your tests as you normally would when using REST Assured and Spring REST Docs, as shown
in the following example:
import io.restassured.specification.RequestSpecification;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.restdocs.AutoConfigureRestDocs;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.web.server.LocalServerPort;
import static io.restassured.RestAssured.given;
import static org.hamcrest.Matchers.is;
import static org.springframework.restdocs.restassured3.RestAssuredRestDocumentation.document;
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class UserDocumentationTests {
    @Test
    void listUsers(@Autowired RequestSpecification documentationSpec, @LocalServerPort int port) {
        given(documentationSpec).filter(document("list-users")).when().port(port).get("/").then().assertThat()
                .statusCode(is(200));
If you require more control over Spring REST Docs configuration than offered by the
attributes of @AutoConfigureRestDocs, a RestDocsRestAssuredConfigurationCustomizer
bean can be used, as shown in the following example:
@TestConfiguration
public static class CustomizationConfiguration implements RestDocsRestAssuredConfigurationCustomizer {
    @Override
    public void customize(RestAssuredRestDocumentationConfigurer configurer) {
        configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
25.3.23. Additional Auto-configuration and Slicing

Each slice provides one or more @AutoConfigure… annotations that namely defines the
auto-configurations that should be included as part of a slice. Additional
auto-configurations can be added by creating a custom @AutoConfigure… annotation or
simply by adding @ImportAutoConfiguration to the test as shown in the following example:
@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration.class)
class ExampleJdbcTests {
25.3.24. User Configuration and Slicing

If you structure your code in a sensible way, your
@SpringBootApplication class is
used by default as
the configuration of your tests.
It then becomes important not to litter the application’s main class with configuration
settings that are specific to a particular area of its functionality.
Assume that you are using Spring Batch and you rely on the auto-configuration for it.
You could define your @SpringBootApplication as follows:
@SpringBootApplication
@EnableBatchProcessing
public class SampleApplication { ... }
Because this class is the source configuration for the test, any slice test actually
tries to start Spring Batch, which is definitely not what you want to do. A recommended
approach is to move that area-specific configuration to a separate @Configuration class
at the same level as your application, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@EnableBatchProcessing
public class BatchConfiguration { ... }
Depending on the complexity of your application, you may either have a single
@Configuration class for your customizations or one class per domain area. The latter
approach lets you enable it in one of your tests, if necessary, with the @Import
annotation.
Test slices exclude @Configuration classes from scanning. For example, for a @WebMvcTest,
the following configuration will not include the given WebMvcConfigurer bean in the application
context loaded by the test slice:
@Configuration
public class WebConfiguration {
    @Bean
    public WebMvcConfigurer testConfigurer() {
        return new WebMvcConfigurer() {
The configuration below will, however, cause the custom WebMvcConfigurer to be loaded
by the test slice.
@Component
public class TestWebMvcConfigurer implements WebMvcConfigurer {
Another source of confusion is classpath scanning. Assume that, while you structured your
code in a sensible way, you need to scan an additional package. Your application may
resemble the following code:
@SpringBootApplication
@ComponentScan({ "com.example.app", "org.acme.another" })
public class SampleApplication { ... }
Doing so effectively overrides the default component scan directive with the side effect
of scanning those two packages regardless of the slice that you chose. For instance, a
@DataJpaTest seems to suddenly scan components and user configurations of your
application. Again, moving the custom directive to a separate class is a good way to fix
this issue.
If this is not an option for you, you can create a @SpringBootConfiguration
somewhere in the hierarchy of your test so that it is used instead. Alternatively, you
can specify a source for your test, which disables the behavior of finding a default one.
25.3.25. Using Spock to Test Spring Boot Applications

If you wish to use Spock to test a Spring Boot application, you should add a dependency
on Spock’s spock-spring module to your application’s build. spock-spring integrates
Spring’s test framework into Spock. It is recommended that you use Spock 1.2 or later to
benefit from a number of improvements to Spock’s Spring Framework and Spring Boot
integration. See the
documentation for Spock’s Spring module for further details.
25.4. Test Utilities

A few test utility classes that are generally useful when testing your application are
packaged as part of spring-boot.
25.4.1. ConfigFileApplicationContextInitializer

ConfigFileApplicationContextInitializer is an ApplicationContextInitializer that you
can apply to your tests to load Spring Boot application.properties files. You can use
it when you do not need the full set of features provided by @SpringBootTest, as shown
in the following example:
@ContextConfiguration(classes = Config.class,
    initializers = ConfigFileApplicationContextInitializer.class)
Using ConfigFileApplicationContextInitializer alone does not provide support for
@Value("${…}") injection. Its only job is to ensure that application.properties
files are loaded into Spring’s Environment. For @Value support, you need to either
additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest,
which auto-configures one for you.
TestPropertyValues lets you quickly add properties to a
ConfigurableEnvironment or ConfigurableApplicationContext. You can call it with
key=value strings, as follows:
TestPropertyValues.of("org=Spring", "name=Boot").applyTo(env);
25.4.3. OutputCapture

OutputCapture is a JUnit Extension that you can use to capture System.out and
System.err output. To use with {@link ExtendWith @ExtendWith}, you can inject
CapturedOutput as an argument to your test class constructor or test method as follows:
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.springframework.boot.test.system.CapturedOutput;
import org.springframework.boot.test.system.OutputCaptureExtension;
import static org.assertj.core.api.Assertions.assertThat;
@ExtendWith(OutputCaptureExtension.class)
class MyTest {
    @Test
    void testName(CapturedOutput output) {
        System.out.println("Hello World!");
        assertThat(output).contains("World"));
Spring Framework 5.0 provides a new WebTestClient that works for
WebFlux integration tests and both
WebFlux and MVC end-to-end testing. It provides a fluent API for assertions,
unlike TestRestTemplate.
TestRestTemplate is a convenience alternative to Spring’s RestTemplate that is useful
in integration tests. You can get a vanilla template or one that sends Basic HTTP
authentication (with a username and password). In either case, the template behaves in a
test-friendly way by not throwing exceptions on server-side errors. It is recommended,
but not mandatory, to use the Apache HTTP Client (version 4.3.2 or better). If you have
that on your classpath, the TestRestTemplate responds by configuring the client
appropriately. If you do use Apache’s HTTP client, some additional test-friendly features
are enabled:
    @Test
    public void testRequest() throws Exception {
        HttpHeaders headers = this.template.getForEntity(
                "https://myhost.example.com/example", String.class).getHeaders();
        assertThat(headers.getLocation()).hasHost("other.example.com");
Alternatively, if you use the @SpringBootTest annotation with
WebEnvironment.RANDOM_PORT or WebEnvironment.DEFINED_PORT, you can inject a
fully configured TestRestTemplate and start using it. If necessary, additional
customizations can be applied through the RestTemplateBuilder bean. Any URLs that do
not specify a host and port automatically connect to the embedded server, as shown in the
following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class SampleWebClientTests {
    @Autowired
    private TestRestTemplate template;
    @Test
    void testRequest() {
        HttpHeaders headers = this.template.getForEntity("/example", String.class).getHeaders();
        assertThat(headers.getLocation()).hasHost("other.example.com");
    @TestConfiguration
    static class Config {
        @Bean
        RestTemplateBuilder restTemplateBuilder() {
            return new RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
                    .setReadTimeout(Duration.ofSeconds(1));
Spring Boot provides WebSockets auto-configuration for embedded Tomcat, Jetty, and
Undertow. If you deploy a war file to a standalone container, Spring Boot assumes that the
container is responsible for the configuration of its WebSocket support.
Spring Framework provides rich WebSocket support
for MVC web applications that can be easily accessed through the
spring-boot-starter-websocket module.
WebSocket support is also available for
reactive web applications and
requires to include the WebSocket API alongside spring-boot-starter-webflux:
<dependency>
    <groupId>javax.websocket</groupId>
    <artifactId>javax.websocket-api</artifactId>
</dependency>
Spring Boot provides Web Services auto-configuration so that all you must do is define
your Endpoints.
The Spring Web Services features can be easily accessed
with the spring-boot-starter-webservices module.
SimpleWsdl11Definition and SimpleXsdSchema beans can be automatically created for
your WSDLs and XSDs respectively. To do so, configure their location, as shown in the
following example:




    

spring.webservices.wsdl-locations=classpath:/wsdl
27.1. Calling Web Services with WebServiceTemplate

If you need to call remote Web services from your application, you can use the
WebServiceTemplate class.
Since WebServiceTemplate instances often need to be customized before being used, Spring
Boot does not provide any single auto-configured WebServiceTemplate bean. It does,
however, auto-configure a WebServiceTemplateBuilder, which can be used to create
WebServiceTemplate instances when needed.
The following code shows a typical example:
@Service
public class MyService {
    private final WebServiceTemplate webServiceTemplate;
    public MyService(WebServiceTemplateBuilder webServiceTemplateBuilder) {
        this.webServiceTemplate = webServiceTemplateBuilder.build();
    public DetailsResp someWsCall(DetailsReq detailsReq) {
         return (DetailsResp) this.webServiceTemplate.marshalSendAndReceive(detailsReq, new SoapActionCallback(ACTION));
By default, WebServiceTemplateBuilder detects a suitable HTTP-based
WebServiceMessageSender using the available HTTP client libraries on the classpath. You
can also customize read and connection timeouts as follows:
@Bean
public WebServiceTemplate webServiceTemplate(WebServiceTemplateBuilder builder) {
    return builder.messageSenders(new HttpWebServiceMessageSenderBuilder()
            .setConnectTimeout(5000).setReadTimeout(2000).build()).build();
If you work in a company that develops shared libraries, or if you work on an open-source
or commercial library, you might want to develop your own auto-configuration.
Auto-configuration classes can be bundled in external jars and still be picked-up by
Spring Boot.
Auto-configuration can be associated to a “starter” that provides the auto-configuration
code as well as the typical libraries that you would use with it. We first cover what
you need to know to build your own auto-configuration and then we move on to the
typical steps required to create a custom starter.
28.1. Understanding Auto-configured Beans

Under the hood, auto-configuration is implemented with standard @Configuration classes.
Additional @Conditional annotations are used to constrain when the auto-configuration
should apply. Usually, auto-configuration classes use @ConditionalOnClass and
@ConditionalOnMissingBean annotations. This ensures that auto-configuration applies
only when relevant classes are found and when you have not declared your own
@Configuration.
You can browse the source code of spring-boot-autoconfigure
to see the @Configuration classes that Spring provides (see the
META-INF/spring.factories
file).
28.2. Locating Auto-configuration Candidates

Spring Boot checks for the presence of a META-INF/spring.factories file within your
published jar. The file should list your configuration classes under the
EnableAutoConfiguration key, as shown in the following example:
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.mycorp.libx.autoconfigure.LibXAutoConfiguration,\
com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration
Auto-configurations must be loaded that way only. Make sure that they are defined in
a specific package space and that they are never the target of component scanning.
Furthermore, auto-configuration classes should not enable component scanning to find
additional components. Specific @Imports should be used instead.
@AutoConfigureAfter or
@AutoConfigureBefore
annotations if your configuration needs to be applied in a specific order. For example,
if you provide web-specific configuration, your class may need to be applied after
WebMvcAutoConfiguration.
If you want to order certain auto-configurations that should not have any direct
knowledge of each other, you can also use @AutoConfigureOrder. That annotation has the
same semantic as the regular @Order annotation but provides a dedicated order for
auto-configuration classes.
28.3. Condition Annotations

You almost always want to include one or more @Conditional annotations on your
auto-configuration class. The @ConditionalOnMissingBean annotation is one common
example that is used to allow developers to override auto-configuration if they are
not happy with your defaults.
Spring Boot includes a number of @Conditional annotations that you can reuse in your
own code by annotating @Configuration classes or individual @Bean methods. These
annotations include:
28.3.1. Class Conditions

The @ConditionalOnClass and @ConditionalOnMissingClass annotations let
@Configuration classes be included based on the presence or absence of specific classes.
Due to the fact that annotation metadata is parsed by using ASM, you
can use the value attribute to refer to the real class, even though that class might not
actually appear on the running application classpath. You can also use the name
attribute if you prefer to specify the class name by using a String value.
This mechanism does not apply the same way to @Bean methods where typically the return
type is the target of the condition: before the condition on the method applies, the JVM
will have loaded the class and potentially processed method references which will fail if
the class is not present.
To handle this scenario, a separate @Configuration class can be used to isolate the
condition, as shown in the following example:
@Configuration(proxyBeanMethods = false)
// Some conditions
public class MyAutoConfiguration {
    // Auto-configured beans
    @Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(EmbeddedAcmeService.class)
    static class EmbeddedConfiguration {
        @Bean
        @ConditionalOnMissingBean
        public EmbeddedAcmeService embeddedAcmeService() { ... }
If you use @ConditionalOnClass or @ConditionalOnMissingClass as a part of a
meta-annotation to compose your own composed annotations, you must use name as referring
to the class in such a case is not handled.
28.3.2. Bean Conditions

The @ConditionalOnBean and @ConditionalOnMissingBean annotations let a bean be
included based on the presence or absence of specific beans. You can use the value
attribute to specify beans by type or name to specify beans by name. The search
attribute lets you limit the ApplicationContext hierarchy that should be considered
when searching for beans.
When placed on a @Bean method, the target type defaults to the return type of the
method, as shown in the following example:
@Configuration(proxyBeanMethods = false)
public class MyAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public MyService myService() { ... }
In the preceding example, the myService bean is going to be created if no bean of type
MyService is already contained in the ApplicationContext.
You need to be very careful about the order in which bean definitions are added, as
these conditions are evaluated based on what has been processed so far. For this reason,
we recommend using only @ConditionalOnBean and @ConditionalOnMissingBean annotations
on auto-configuration classes (since these are guaranteed to load after any user-defined
bean definitions have been added).
@ConditionalOnBean and @ConditionalOnMissingBean do not prevent @Configuration
classes from being created. The only difference between using these conditions at the class level
and marking each contained @Bean method with the annotation is that the former prevents
registration of the @Configuration class as a bean if the condition does not match.
28.3.3. Property Conditions

The @ConditionalOnProperty annotation lets configuration be included based on a Spring
Environment property. Use the prefix and name attributes to specify the property that
should be checked. By default, any property that exists and is not equal to false is
matched. You can also create more advanced checks by using the havingValue and
matchIfMissing attributes.
28.3.4. Resource Conditions

The @ConditionalOnResource annotation lets configuration be included only when a
specific resource is present. Resources can be specified by using the usual Spring
conventions, as shown in the following example: file:/home/user/test.dat.
28.3.5. Web Application Conditions

The @ConditionalOnWebApplication and @ConditionalOnNotWebApplication annotations let
configuration be included depending on whether the application is a “web application”.
A web application is any application that uses a Spring WebApplicationContext,
defines a session scope, or has a StandardServletEnvironment.
28.3.6. SpEL Expression Conditions

The @ConditionalOnExpression annotation lets configuration be included based on the
result of a SpEL expression.
28.4. Testing your Auto-configuration

An auto-configuration can be affected by many factors: user configuration (@Bean
definition and Environment customization), condition evaluation (presence of a
particular library), and others. Concretely, each test should create a well defined
ApplicationContext that represents a combination of those customizations.
ApplicationContextRunner provides a great way to achieve that.
ApplicationContextRunner is usually defined as a field of the test class to gather the
base, common configuration. The following example makes sure that
UserServiceAutoConfiguration is always invoked:
private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
        .withConfiguration(AutoConfigurations.of(UserServiceAutoConfiguration.class));
If multiple auto-configurations have to be defined, there is no need to order their
declarations as they are invoked in the exact same order as when running the
application.
Each test can use the runner to represent a particular use case. For instance, the sample
below invokes a user configuration (UserConfiguration) and checks that the
auto-configuration backs off properly. Invoking run provides a callback context that can
be used with Assert4J.
@Test
void defaultServiceBacksOff() {
    this.contextRunner.withUserConfiguration(UserConfiguration.class).run((context) -> {
        assertThat(context).hasSingleBean(UserService.class);
        assertThat(context).getBean("myUserService").isSameAs(context.getBean(UserService.class));
@Configuration(proxyBeanMethods = false)
static class UserConfiguration {
    @Bean
    UserService myUserService() {
        return new UserService("mine");
It is also possible to easily customize the Environment, as shown in the following
example:
@Test
void serviceNameCanBeConfigured() {
    this.contextRunner.withPropertyValues("user.name=test123").run((context) -> {
        assertThat(context).hasSingleBean(UserService.class);
        assertThat(context.getBean(UserService.class).getName()).isEqualTo("test123");
The runner can also be used to display the ConditionEvaluationReport. The report can be printed
at INFO or DEBUG level. The following example shows how to use the ConditionEvaluationReportLoggingListener
to print the report in auto-configuration tests.
@Test
public void autoConfigTest {
    ConditionEvaluationReportLoggingListener initializer = new ConditionEvaluationReportLoggingListener(
            LogLevel.INFO);
    ApplicationContextRunner contextRunner = new ApplicationContextRunner()
            .withInitializer(initializer).run((context) -> {
                    // Do something...
28.4.1. Simulating a Web Context

If you need to test an auto-configuration that only operates in a Servlet or Reactive web
application context, use the WebApplicationContextRunner or
ReactiveWebApplicationContextRunner respectively.
28.4.2. Overriding the Classpath

It is also possible to test what happens when a particular class and/or package is not
present at runtime. Spring Boot ships with a FilteredClassLoader that can easily be used
by the runner. In the following example, we assert that if UserService is not present, the
auto-configuration is properly disabled:
@Test
void serviceIsIgnoredIfLibraryIsNotPresent() {
    this.contextRunner.withClassLoader(new FilteredClassLoader(UserService.class))
            .run((context) -> assertThat(context).doesNotHaveBean("userService"));
The starter module that provides a dependency to the autoconfigure module as well
as the library and any additional dependencies that are typically useful. In a nutshell,
adding the starter should provide everything needed to start using that library.




    

28.5.1. Naming

You should make sure to provide a proper namespace for your starter. Do not start your
module names with spring-boot, even if you use a different Maven groupId. We may
offer official support for the thing you auto-configure in the future.
As a rule of thumb, you should name a combined module after the starter. For example,
assume that you are creating a starter for "acme" and that you name the auto-configure
module acme-spring-boot-autoconfigure and the starter acme-spring-boot-starter. If
you only have one module that combines the two, name it acme-spring-boot-starter.
28.5.2. Configuration keys

If your starter provides configuration keys, use a unique namespace for them. In
particular, do not include your keys in the namespaces that Spring Boot uses (such as
server, management, spring, and so on). If you use the same namespace, we may modify
these namespaces in the future in ways that break your modules. As a rule of thumb,
prefix all your keys with a namespace that you own (e.g. acme).
Make sure that configuration keys are documented by adding field javadoc for each
property, as shown in the following example:
@ConfigurationProperties("acme")
public class AcmeProperties {
     * Whether to check the location of acme resources.
    private boolean checkLocation = true;
     * Timeout for establishing a connection to the acme server.
    private Duration loginTimeout = Duration.ofSeconds(3);
    // getters & setters
Here are some rules we follow internally to make sure descriptions are consistent:
Use java.time.Duration rather than long and describe the default unit if it differs
from milliseconds, e.g. "If a duration suffix is not specified, seconds will be used".
Do not provide the default value in the description unless it has to be determined at
runtime.
Make sure to
trigger meta-data
generation so that IDE assistance is available for your keys as well. You may want to
review the generated metadata (META-INF/spring-configuration-metadata.json) to make
sure your keys are properly documented. Using your own starter in a compatible IDE is
also a good idea to validate that quality of the metadata.
28.5.3. autoconfigure Module

The autoconfigure module contains everything that is necessary to get started with the
library. It may also contain configuration key definitions (such as
@ConfigurationProperties) and any callback interface that can be used to further
customize how the components are initialized.
You should mark the dependencies to the library as optional so that you can include
the autoconfigure module in your projects more easily. If you do it that way, the
library is not provided and, by default, Spring Boot backs off.
Spring Boot uses an annotation processor to collect the conditions on auto-configurations
in a metadata file (META-INF/spring-autoconfigure-metadata.properties). If that file is
present, it is used to eagerly filter auto-configurations that do not match, which will
improve startup time. It is recommended to add the following dependency in a module that
contains auto-configurations:
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-autoconfigure-processor</artifactId>
    <optional>true</optional>
</dependency>
With Gradle 4.5 and earlier, the dependency should be declared in the compileOnly
configuration, as shown in the following example:
dependencies {
    compileOnly "org.springframework.boot:spring-boot-autoconfigure-processor"
With Gradle 4.6 and later, the dependency should be declared in the annotationProcessor
configuration, as shown in the following example:
dependencies {
    annotationProcessor "org.springframework.boot:spring-boot-autoconfigure-processor"
28.5.4. Starter Module

The starter is really an empty jar. Its only purpose is to provide the necessary
dependencies to work with the library. You can think of it as an opinionated view of what
is required to get started.
Do not make assumptions about the project in which your starter is added. If the library
you are auto-configuring typically requires other starters, mention them as well.
Providing a proper set of default dependencies may be hard if the number of optional
dependencies is high, as you should avoid including dependencies that are unnecessary for
a typical usage of the library. In other words, you should not include optional
dependencies.
Either way, your starter must reference the core Spring Boot starter
(spring-boot-starter) directly or indirectly (i.e. no need to add it if your starter
relies on another starter). If a project is created with only your custom starter, Spring
Boot’s core features will be honoured by the presence of the core starter.
Kotlin is a statically-typed language targeting the JVM (and other
platforms) which allows writing concise and elegant code while providing
interoperability with existing libraries written
in Java.
Spring Boot provides Kotlin support by leveraging the support in other Spring projects
such as Spring Framework, Spring Data, and Reactor. See the
Spring Framework Kotlin support documentation
for more information.
The easiest way to start with Spring Boot and Kotlin is to follow
this comprehensive tutorial. You
can create new Kotlin projects via
start.spring.io. Feel free to join the #spring
channel of Kotlin Slack or ask a question with the spring
and kotlin tags on Stack
Overflow if you need support.
29.1. Requirements

Spring Boot supports Kotlin 1.3.x. To use Kotlin, org.jetbrains.kotlin:kotlin-stdlib and
org.jetbrains.kotlin:kotlin-reflect must be present on the classpath. The
kotlin-stdlib variants kotlin-stdlib-jdk7 and kotlin-stdlib-jdk8 can also be used.
Since Kotlin classes are
final by default, you are likely to want to configure
kotlin-spring
plugin in order to automatically open Spring-annotated classes so that they can be
proxied.
Jackson’s Kotlin module is required
for serializing / deserializing JSON data in Kotlin. It is automatically registered when
found on the classpath. A warning message is logged if Jackson and Kotlin are present but
the Jackson Kotlin module is not.
One of Kotlin’s key features is null-safety. It
deals with null values at compile time rather than deferring the problem to runtime and
encountering a NullPointerException. This helps to eliminate a common source of bugs
without paying the cost of wrappers like Optional. Kotlin also allows using functional
constructs with nullable values as described in this
comprehensive guide to null-safety in Kotlin.
Although Java does not allow one to express null-safety in its type system, Spring
Framework, Spring Data, and Reactor now provide null-safety of their API via
tooling-friendly annotations. By default, types from Java APIs used in Kotlin are
recognized as
platform types
for which null-checks are relaxed.
Kotlin’s support for JSR 305
annotations combined with nullability annotations provide null-safety for the related
Spring API in Kotlin.
The JSR 305 checks can be configured by adding the -Xjsr305 compiler flag with the
following options: -Xjsr305={strict|warn|ignore}. The default behavior is the same as
-Xjsr305=warn. The strict value is required to have null-safety taken in account in
Kotlin types inferred from Spring API but should be used with the knowledge that Spring
API nullability declaration could evolve even between minor releases and more checks may
be added in the future).
Generic type arguments, varargs and array elements nullability are not yet
supported. See SPR-15942 for up-to-date
information. Also be aware that Spring Boot’s own API is not yet
annotated.
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.runApplication
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
    runApplication<MyApplication>(*args)
This is a drop-in replacement for
SpringApplication.run(MyApplication::class.java, *args). It also allows customization
of the application as shown in the following example:
runApplication<MyApplication>(*args) {
    setBannerMode(OFF)
Kotlin extensions provide the ability
to extend existing classes with additional functionality. The Spring Boot Kotlin API makes
use of these extensions to add new Kotlin specific conveniences to existing APIs.
TestRestTemplate extensions, similar to those provided by Spring Framework for
RestOperations in Spring Framework, are provided. Among other things, the extensions
make it possible to take advantage of Kotlin reified type parameters.
29.4. Dependency management

In order to avoid mixing different versions of Kotlin dependencies on the classpath,
Spring Boot imports the Kotlin BOM.
With Maven, the Kotlin version can be customized via the kotlin.version property and
plugin management is provided for kotlin-maven-plugin. With Gradle, the Spring Boot
plugin automatically aligns the kotlin.version with the version of the Kotlin plugin.
29.5. @ConfigurationProperties

@ConfigurationProperties supports classes with immutable val properties as shown in
the following example:
@ConfigurationProperties("example.kotlin")
data class KotlinExampleProperties(
        val name: String,
        val description: String,
        val myService: MyService
data class MyService(
    val apiToken: String,
    val uri: URI
To generate your own
metadata using the annotation processor, kapt should
be configured with the spring-boot-configuration-processor dependency. Note that some
features (such as detecting the default value or deperecated items) are not working due
to limitations in the model kapt provides.
29.6. Testing

While it is possible to use JUnit 4 to test Kotlin code, JUnit 5 is recommended. JUnit 5
enables a test class to be instantiated once and reused for all of the class’s tests. This
makes it possible to use @BeforeClass and @AfterClass annotations on non-static
methods, which is a good fit for Kotlin.
JUnit 5 is the default and the vintage engine is provided for backward compatibility with
JUnit 4. If you don’t use it, exclude org.junit.vintange:junit-vintage-engine. See the
JUnit 5 documentation
for more details. You also need to
switch test
instance lifecycle to "per-class".
To mock Kotlin classes, MockK is recommended. If you need the Mockk
equivalent of the Mockito specific
@MockBean and @SpyBean
annotations, you can use SpringMockK which
provides similar @MockkBean and @SpykBean annotations.
29.7. Resources

29.7.1. Further reading

Kotlin language reference
Kotlin Slack (with a dedicated #spring channel)
Stackoverflow with spring and kotlin tags
Try Kotlin in your browser
Kotlin blog
Awesome Kotlin
Tutorial: building web applications with Spring Boot and Kotlin
Developing Spring Boot applications with Kotlin
A Geospatial Messenger with Kotlin, Spring Boot and PostgreSQL
Introducing Kotlin support in Spring Framework 5.0
Spring Framework 5 Kotlin APIs, the functional way
spring-kotlin-fullstack: WebFlux Kotlin fullstack example with Kotlin2js for frontend instead of JavaScript or TypeScript
spring-petclinic-kotlin: Kotlin version of the Spring PetClinic Sample Application
spring-kotlin-deepdive: a step by step migration for Boot 1.0 + Java to Boot 2.0 + Kotlin
If you want to learn more about any of the classes discussed in this section, you can
check out the Spring Boot API documentation or you can browse the
source code directly. If you have specific questions, take a look at the
how-to section.
If you are comfortable with Spring Boot’s core features, you can continue on and read
about production-ready features.

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