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Java applications have a notoriously slow startup and a long warmup time. The CRaC (Coordinated Restore at Checkpoint) project from OpenJDK can help improve these issues by creating a checkpoint with an application's peak performance and restoring an instance of the JVM to that point.

To take full advantage of this feature, BellSoft provides containers that are highly optimized for Java applications. These package Alpaquita Linux (a full-featured OS optimized for Java and cloud environment) and Liberica JDK (an open-source Java runtime based on OpenJDK).

These ready-to-use images allow us to easily integrate CRaC in a Spring Boot application:

Improve Java application performance with CRaC support

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DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema .

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And, of course, it can be heavily visual, allowing you to interact with the database using diagrams, visually compose queries, explore the data, generate random data, import data or build HTML5 database reports.

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1. Overview

In an earlier tutorial, we learned about the basics of Spring component scans .

In this write-up, we’ll see the different types of filter options available with the @ComponentScan annotation .

2. @ ComponentScan Filter

By default, classes annotated with @Component, @Repository, @Service, @Controller are registered as Spring beans . The same goes for classes annotated with a custom annotation that is annotated with @Component . We can extend this behavior by using includeFilters and excludeFilters parameters of the @ComponentScan annotation.

There are five types of filters available for ComponentScan.Filter :

  • ANNOTATION
  • ASSIGNABLE_TYPE
  • ASPECTJ
  • REGEX
  • CUSTOM
  • We’ll see these in detail in the next sections.

    We should note that all these filters can include or exclude classes from scanning. For simplicity in our examples, we’ll only include classes.

    3. FilterType.ANNOTATION

    The ANNOTATION filter type includes or excludes classes in the component scans which are marked with given annotations.

    Let’s say, for example, that we have an @Anima l annotation:

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    public @interface Animal { }

    Now, let’s define an Elephant class which uses @Animal :

    @Animal
    public class Elephant { }

    Finally, let’s use the FilterType.ANNOTATION to tell Spring to scan for @Animal -annotated classes:

    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.ANNOTATION,
            classes = Animal.class))
    public class ComponentScanAnnotationFilterApp { }

    As we can see, the scanner picks up our Elephant just fine:

    @Test
    public void whenAnnotationFilterIsUsed_thenComponentScanShouldRegisterBeanAnnotatedWithAnimalAnootation() {
        ApplicationContext applicationContext =
                new AnnotationConfigApplicationContext(ComponentScanAnnotationFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
                .filter(bean -> !bean.contains("org.springframework")
                        && !bean.contains("componentScanAnnotationFilterApp"))
                .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.get(0), equalTo("elephant"));
    

    4. FilterType.ASSIGNABLE_TYPE

    The ASSIGNABLE_TYPE filters all classes during the component scan that either extend the class or implement the interface of the specified type.

    First, let’s declare the Animal interface:

    public interface Animal { }

    And again, let’s declare our Elephant class, this time implementing Animal interface:

    public class Elephant implements Animal { }

    Let’s declare our Cat class that also implementing Animal:

    public class Cat implements Animal { }

    Now, let’s use ASSIGNABLE_TYPE to guide Spring to scan for Animal-implementing classes:

    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE,
            classes = Animal.class))
    public class ComponentScanAssignableTypeFilterApp { }

    And we’ll see that both Cat and Elephant get scanned:

    @Test
    public void whenAssignableTypeFilterIsUsed_thenComponentScanShouldRegisterBean() {
        ApplicationContext applicationContext =
          new AnnotationConfigApplicationContext(ComponentScanAssignableTypeFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework")
            && !bean.contains("componentScanAssignableTypeFilterApp"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(2));
        assertThat(beans.contains("cat"), equalTo(true));
        assertThat(beans.contains("elephant"), equalTo(true));
    

    5. FilterType.REGEX

    The REGEX filter checks if the class name matching a given regex pattern. FilterType.REGEX checks both simple and fully-qualified class names.

    Once again, let’s declare our Elephant class. This time not implementing any interface or annotated with any annotation:

    public class Elephant { }

    Let’s declare one more class Cat:

    public class Cat { }

    Now, let’s declare Lion class:

    public class Lion { }

    Let’s use FilterType.REGEX which instructs Spring to scan classes that match regex .*[nt]. Our regex expression evaluates everything containing nt:

    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.REGEX,
            pattern = ".*[nt]"))
    public class ComponentScanRegexFilterApp { }

    This time in our test, we’ll see that Spring scans the Elephant, but not the Lion:

    @Test
    public void whenRegexFilterIsUsed_thenComponentScanShouldRegisterBeanMatchingRegex() {
        ApplicationContext applicationContext =
          new AnnotationConfigApplicationContext(ComponentScanRegexFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework")
            && !bean.contains("componentScanRegexFilterApp"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.contains("elephant"), equalTo(true));
    

    6. FilterType.ASPECTJ

    When we want to use expressions to pick out a complex subset of classes, we need to use the FilterType ASPECTJ.

    For this use case, we can reuse the same three classes as in the previous section.

    Let’s use FilterType.ASPECTJ to direct Spring to scan classes that match our AspectJ expression:

    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.ASPECTJ,
      pattern = "com.baeldung.componentscan.filter.aspectj.* "
      + "&& !(com.baeldung.componentscan.filter.aspectj.L* "
      + "|| com.baeldung.componentscan.filter.aspectj.C*)"))
    public class ComponentScanAspectJFilterApp { }

    While a bit complex, our logic here wants beans that start with neither “L” nor “C” in their class name, so that leaves us with Elephants again:

    @Test
    public void whenAspectJFilterIsUsed_thenComponentScanShouldRegisterBeanMatchingAspectJCreteria() {
        ApplicationContext applicationContext =
          new AnnotationConfigApplicationContext(ComponentScanAspectJFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework")
            && !bean.contains("componentScanAspectJFilterApp"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.get(0), equalTo("elephant"));
    

    7. FilterType.CUSTOM

    If none of the above filter types meet our requirement then we can also create a custom filter type. For example, let’s say we only want to scan classes whose name is five characters or shorter.

    To create a custom filter, we need to implement the org.springframework.core.type.filter.TypeFilter:

    public class ComponentScanCustomFilter implements TypeFilter {
        @Override
        public boolean match(MetadataReader metadataReader,
          MetadataReaderFactory metadataReaderFactory) throws IOException {
            ClassMetadata classMetadata = metadataReader.getClassMetadata();
            String fullyQualifiedName = classMetadata.getClassName();
            String className = fullyQualifiedName.substring(fullyQualifiedName.lastIndexOf(".") + 1);
            return className.length() > 5 ? true : false;
    

    Let’s use FilterType.CUSTOM which conveys Spring to scan classes using our custom filter ComponentScanCustomFilter:

    @Configuration
    @ComponentScan(includeFilters = @ComponentScan.Filter(type = FilterType.CUSTOM,
      classes = ComponentScanCustomFilter.class))
    public class ComponentScanCustomFilterApp { }

    Now it’s time to see test case of our custom filter ComponentScanCustomFilter:

    @Test
    public void whenCustomFilterIsUsed_thenComponentScanShouldRegisterBeanMatchingCustomFilter() {
        ApplicationContext applicationContext =
          new AnnotationConfigApplicationContext(ComponentScanCustomFilterApp.class);
        List<String> beans = Arrays.stream(applicationContext.getBeanDefinitionNames())
          .filter(bean -> !bean.contains("org.springframework")
            && !bean.contains("componentScanCustomFilterApp")
            && !bean.contains("componentScanCustomFilter"))
          .collect(Collectors.toList());
        assertThat(beans.size(), equalTo(1));
        assertThat(beans.get(0), equalTo("elephant"));
    

    8. Summary

    In this tutorial, we introduced filters associated with @ComponentScan.

    As usual, the complete code is available over on GitHub.

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    Partner – DBSchema – NPI EA (tag = Spring Data JPA)
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    DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema.

    The way it does all of that is by using a design model, a database-independent image of the schema, which can be shared in a team using GIT and compared or deployed on to any database.

    And, of course, it can be heavily visual, allowing you to interact with the database using diagrams, visually compose queries, explore the data, generate random data, import data or build HTML5 database reports.

    Take a look at DBSchema

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