URL (Java Platform SE 7 )

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implements Serializable

Class

URL

represents a Uniform Resource Locator, a pointer to a "resource" on the World Wide Web. A resource can be something as simple as a file or a directory, or it can be a reference to a more complicated object, such as a query to a database or to a search engine. More information on the types of URLs and their formats can be found at: Types of URL In general, a URL can be broken into several parts. Consider the following example: http://www.example.com/docs/resource1.html The URL above indicates that the protocol to use is


    http

(HyperText Transfer Protocol) and that the information resides on a host machine named


    www.example.com

. The information on that host machine is named


    /docs/resource1.html

. The exact meaning of this name on the host machine is both protocol dependent and host dependent. The information normally resides in a file, but it could be generated on the fly. This component of the URL is called the path component. A URL can optionally specify a "port", which is the port number to which the TCP connection is made on the remote host machine. If the port is not specified, the default port for the protocol is used instead. For example, the default port for


    http

. An alternative port could be specified as: http://www.example.com:1080/docs/resource1.html The syntax of

URL

is defined by RFC 2396: Uniform Resource Identifiers (URI): Generic Syntax , amended by RFC 2732: Format for Literal IPv6 Addresses in URLs . The Literal IPv6 address format also supports scope_ids. The syntax and usage of scope_ids is described here . A URL may have appended to it a "fragment", also known as a "ref" or a "reference". The fragment is indicated by the sharp sign character "#" followed by more characters. For example, http://java.sun.com/index.html#chapter1 This fragment is not technically part of the URL. Rather, it indicates that after the specified resource is retrieved, the application is specifically interested in that part of the document that has the tag


    chapter1

attached to it. The meaning of a tag is resource specific. An application can also specify a "relative URL", which contains only enough information to reach the resource relative to another URL. Relative URLs are frequently used within HTML pages. For example, if the contents of the URL: http://java.sun.com/index.html contained within it the relative URL: FAQ.html it would be a shorthand for: http://java.sun.com/FAQ.html The relative URL need not specify all the components of a URL. If the protocol, host name, or port number is missing, the value is inherited from the fully specified URL. The file component must be specified. The optional fragment is not inherited. The URL class does not itself encode or decode any URL components according to the escaping mechanism defined in RFC2396. It is the responsibility of the caller to encode any fields, which need to be escaped prior to calling URL, and also to decode any escaped fields, that are returned from URL. Furthermore, because URL has no knowledge of URL escaping, it does not recognise equivalence between the encoded or decoded form of the same URL. For example, the two URLs:

    http://foo.com/hello world/ and http://foo.com/hello%20world

would be considered not equal to each other. Note, the

URI

class does perform escaping of its component fields in certain circumstances. The recommended way to manage the encoding and decoding of URLs is to use

URI

, and to convert between these two classes using


     toURI()

and


     URI.toURL()

. The


     URLEncoder

and


     URLDecoder

classes can also be used, but only for HTML form encoding, which is not the same as the encoding scheme defined in RFC2396.

Since:: JDK1.0
See Also:: Serialized Form

String spec, URLStreamHandler handler)

Creates a URL by parsing the given spec with the specified handler within a specified context.


   
    
     openConnection
    
   
   ()

Returns a


     URLConnection

instance that represents a connection to the remote object referred to by the

URL


   
    URLConnection


   
    
     openConnection
    
   
   (
   
    Proxy
   
   proxy)

Same as


     openConnection()

, except that the connection will be made through the specified proxy; Protocol handlers that do not support proxing will ignore the proxy parameter and make a normal connection.


   
    InputStream


   
    
     openStream
    
   
   ()

Opens a connection to this

URL

and returns an


    InputStream

for reading from that connection.


   boolean


   
    
     sameFile
    
   
   (
   
    URL
   
   other)

Compares two URLs, excluding the fragment component.


   protected void


   
    
     set
    
   
   (
   
    String
   
   protocol,
   
    String
   
   host,
   int port,
   
    String
   
   file,
   
    String
   
   ref)

Sets the fields of the URL.


   protected void


   
    
     set
    
   
   (
   
    String
   
   protocol,
   
    String
   
   host,
   int port,
   
    String
   
   authority,
   
    String
   
   userInfo,
   
    String
   
   path,
   
    String
   
   query,
   
    String
   
   ref)

Sets the specified 8 fields of the URL.


   static void


   
    
     setURLStreamHandlerFactory
    
   
   (
   
    URLStreamHandlerFactory
   
   fac)

Sets an application's


    URLStreamHandlerFactory


   
    String


   
    
     toExternalForm
    
   
   ()

Constructs a string representation of this

URL


   
    String


   
    
     toString
    
   
   ()

Constructs a string representation of this

URL


   
    
     toURI
    
   
   ()

Returns a

URI

equivalent to this URL.

throws MalformedURLException

Creates a

URL

object from the specified


    protocol


    host


    port

number, and


    file

host can be expressed as a host name or a literal IP address. If IPv6 literal address is used, it should be enclosed in square brackets ( '[' and ']' ), as specified by RFC 2732 ; However, the literal IPv6 address format defined in RFC 2373: IP Version 6 Addressing Architecture is also accepted.

Specifying a port number of -1 indicates that the URL should use the default port for the protocol.

If this is the first URL object being created with the specified protocol, a stream protocol handler object, an instance of class URLStreamHandler , is created for that protocol:

If the application has previously set up an instance of


     URLStreamHandlerFactory

as the stream handler factory, then the


     createURLStreamHandler

method of that instance is called with the protocol string as an argument to create the stream protocol handler.

If no


     URLStreamHandlerFactory

has yet been set up, or if the factory's


     createURLStreamHandler

method returns


     null

, then the constructor finds the value of the system property: java.protocol.handler.pkgs If the value of that system property is not


     null

, it is interpreted as a list of packages separated by a vertical slash character '

'. The constructor tries to load the class named: < package >.< protocol >.Handler where < package > is replaced by the name of the package and < protocol > is replaced by the name of the protocol. If this class does not exist, or if the class exists but it is not a subclass of


     URLStreamHandler

, then the next package in the list is tried.

If the previous step fails to find a protocol handler, then the constructor tries to load from a system default package. < system default package >.< protocol >.Handler If this class does not exist, or if the class exists but it is not a subclass of


     URLStreamHandler

, then a


     MalformedURLException

is thrown.

Protocol handlers for the following protocols are guaranteed to exist on the search path :- http, https, ftp, file, and jar Protocol handlers for additional protocols may also be available.

No validation of the inputs is performed by this constructor.

Parameters:: protocol - the name of the protocol to use.; host - the name of the host.; port - the port number on the host.; file - the file on the host
Throws:: MalformedURLException - if an unknown protocol is specified.
See Also:: System.getProperty(java.lang.String) , setURLStreamHandlerFactory( java.net.URLStreamHandlerFactory) , URLStreamHandler , URLStreamHandlerFactory.createURLStreamHandler( java.lang.String)

throws MalformedURLException

Creates a URL from the specified


    protocol

name,


    host

name, and


    file

name. The default port for the specified protocol is used. This method is equivalent to calling the four-argument constructor with the arguments being


    protocol


    host

-1

, and


    file

. No validation of the inputs is performed by this constructor.

Parameters:: protocol - the name of the protocol to use.; host - the name of the host.; file - the file on the host.
Throws:: MalformedURLException - if an unknown protocol is specified.
See Also:: URL(java.lang.String, java.lang.String, int, java.lang.String)

URLStreamHandler handler) throws MalformedURLException

Creates a

URL

object from the specified


    protocol


    host


    port

number,


    file

, and


    handler

. Specifying a


    port

number of

-1

indicates that the URL should use the default port for the protocol. Specifying a


    handler


    null

indicates that the URL should use a default stream handler for the protocol, as outlined java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String)

If the handler is not null and there is a security manager, the security manager's checkPermission method is called with a NetPermission("specifyStreamHandler") permission. This may result in a SecurityException. No validation of the inputs is performed by this constructor.

Parameters:: protocol - the name of the protocol to use.; host - the name of the host.; port - the port number on the host.; file - the file on the host; handler - the stream handler for the URL.
Throws:: MalformedURLException - if an unknown protocol is specified.; SecurityException - if a security manager exists and its checkPermission method doesn't allow specifying a stream handler explicitly.
See Also:: System.getProperty(java.lang.String) , setURLStreamHandlerFactory( java.net.URLStreamHandlerFactory) , URLStreamHandler , URLStreamHandlerFactory.createURLStreamHandler( java.lang.String) , SecurityManager.checkPermission(java.security.Permission) , NetPermission

public URL(String spec)
    throws MalformedURLException

Creates a

URL

object from the


    String

representation. This constructor is equivalent to a call to the two-argument constructor with a


    null

first argument.

Parameters:: spec - the String to parse as a URL.
Throws:: MalformedURLException - if no protocol is specified, or an unknown protocol is found, or spec is null .
See Also:: URL(java.net.URL, java.lang.String)

String spec) throws MalformedURLException

Creates a URL by parsing the given spec within a specified context. The new URL is created from the given context URL and the spec argument as described in RFC2396 "Uniform Resource Identifiers : Generic * Syntax" : <scheme>://<authority><path>?<query>#<fragment> The reference is parsed into the scheme, authority, path, query and fragment parts. If the path component is empty and the scheme, authority, and query components are undefined, then the new URL is a reference to the current document. Otherwise, the fragment and query parts present in the spec are used in the new URL. If the scheme component is defined in the given spec and does not match the scheme of the context, then the new URL is created as an absolute URL based on the spec alone. Otherwise the scheme component is inherited from the context URL. If the authority component is present in the spec then the spec is treated as absolute and the spec authority and path will replace the context authority and path. If the authority component is absent in the spec then the authority of the new URL will be inherited from the context. If the spec's path component begins with a slash character "/" then the path is treated as absolute and the spec path replaces the context path. Otherwise, the path is treated as a relative path and is appended to the context path, as described in RFC2396. Also, in this case, the path is canonicalized through the removal of directory changes made by occurences of ".." and ".". For a more detailed description of URL parsing, refer to RFC2396.

Parameters:: context - the context in which to parse the specification.; spec - the String to parse as a URL.
Throws:: MalformedURLException - if no protocol is specified, or an unknown protocol is found, or spec is null .
See Also:: URL(java.lang.String, java.lang.String, int, java.lang.String) , URLStreamHandler , URLStreamHandler.parseURL(java.net.URL, java.lang.String, int, int)

URLStreamHandler handler) throws MalformedURLException

Creates a URL by parsing the given spec with the specified handler within a specified context. If the handler is null, the parsing occurs as with the two argument constructor.

Parameters:: context - the context in which to parse the specification.; spec - the String to parse as a URL.; handler - the stream handler for the URL.
Throws:: MalformedURLException - if no protocol is specified, or an unknown protocol is found, or spec is null .; SecurityException - if a security manager exists and its checkPermission method doesn't allow specifying a stream handler.
See Also:: URL(java.lang.String, java.lang.String, int, java.lang.String) , URLStreamHandler , URLStreamHandler.parseURL(java.net.URL, java.lang.String, int, int)

String ref)

Sets the fields of the URL. This is not a public method so that only URLStreamHandlers can modify URL fields. URLs are otherwise constant.

Parameters:: protocol - the name of the protocol to use; host - the name of the host; port - the port number on the host; file - the file on the host; ref - the internal reference in the URL

String query, String ref)

Sets the specified 8 fields of the URL. This is not a public method so that only URLStreamHandlers can modify URL fields. URLs are otherwise constant.

Parameters:: protocol - the name of the protocol to use; host - the name of the host; port - the port number on the host; authority - the authority part for the url; userInfo - the username and password; path - the file on the host; ref - the internal reference in the URL; query - the query part of this URL
Since:

getDefaultPort

equals

sameFile

toExternalForm

setURLStreamHandlerFactory