Class URL

java.lang.Object
java.net.URL
All Implemented Interfaces:
Serializable
public final class URL extends Object 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 is 80. 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://www.example.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://www.example.com/index.html
contained within it the relative URL: 
    FAQ.html
it would be a shorthand for: 
    http://www.example.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.

Constructing instances of URL

The java.net.URL constructors are deprecated. Developers are encouraged to use java.net.URI to parse or construct a URL. In cases where an instance of java.net.URL is needed to open a connection, URI can be used to construct or parse the URL string, possibly calling URI.parseServerAuthority() to validate that the authority component can be parsed as a server-based authority, and then calling URI.toURL() to create the URL instance.

The URL constructors are specified to throw MalformedURLException but the actual parsing/validation that is performed is implementation dependent. Some parsing/validation may be delayed until later, when the underlying stream handler's implementation is called. Being able to construct an instance of URL doesn't provide any guarantee about its conformance to the URL syntax specification.

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.

API Note:
Applications working with file paths and file URIs should take great care to use the appropriate methods to convert between the two. The Path.of(URI) factory method and the File(URI) constructor can be used to create Path or File objects from a file URI. Path.toUri() and File.toURI() can be used to create a URI from a file path, which can be converted to URL using URI.toURL(). Applications should never try to construct or parse a URL from the direct string representation of a File or Path instance.

Before constructing a URL from a URI, and depending on the protocol involved, applications should consider validating whether the URI authority can be parsed as server-based.

Some components of a URL or URI, such as userinfo, may be abused to construct misleading URLs or URIs. Applications that deal with URLs or URIs should take into account the recommendations advised in RFC3986, Section 7, Security Considerations.

All URL constructors may throw MalformedURLException. In particular, if the underlying URLStreamHandler implementation rejects, or is known to reject, any of the parameters, MalformedURLException may be thrown. Typically, a constructor that calls the stream handler's parseURL method may throw MalformedURLException if the underlying stream handler implementation of that method throws IllegalArgumentException. However, which checks are performed, or not, by the stream handlers is implementation dependent, and callers should not rely on such checks for full URL validation.

Since:
1.0
External Specifications
See Also:

  • Constructor Summary

    Constructors
    Constructor
    Description
    URL(String spec)
    Deprecated.
    Use URI.toURL() to construct an instance of URL.
    URL(String protocol, String host, int port, String file)
    Deprecated.
    Use URI.toURL() to construct an instance of URL.
    URL(String protocol, String host, int port, String file, URLStreamHandler handler)
    Deprecated.
    Use of(URI, URLStreamHandler) to construct an instance of URL associated with a custom protocol handler.
    URL(String protocol, String host, String file)
    Deprecated.
    Use URI.toURL() to construct an instance of URL.
    URL(URL context, String spec)
    Deprecated.
    Use URI.toURL() to construct an instance of URL.
    URL(URL context, String spec, URLStreamHandler handler)
    Deprecated.
    Use of(URI, URLStreamHandler) to construct an instance of URL associated with a custom protocol handler.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    equals(Object obj)
    Compares this URL for equality with another object.
    String
    getAuthority()
    Gets the authority part of this URL.
    final Object
    getContent()
    Gets the contents of this URL.
    final Object
    getContent(Class<?>[] classes)
    Gets the contents of this URL.
    int
    getDefaultPort()
    Gets the default port number of the protocol associated with this URL.
    String
    getFile()
    Gets the file name of this URL.
    String
    getHost()
    Gets the host name of this URL, if applicable.
    String
    getPath()
    Gets the path part of this URL.
    int
    getPort()
    Gets the port number of this URL.
    String
    getProtocol()
    Gets the protocol name of this URL.
    String
    getQuery()
    Gets the query part of this URL.
    String
    getRef()
    Gets the anchor (also known as the "reference") of this URL.
    String
    getUserInfo()
    Gets the userInfo part of this URL.
    int
    hashCode()
    Creates an integer suitable for hash table indexing.
    static URL
    of(URI uri, URLStreamHandler handler)
    Creates a URL from a URI, as if by invoking uri.toURL(), but associating it with the given URLStreamHandler, if allowed.
    URLConnection
    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 proxying will ignore the proxy parameter and make a normal connection.
    final 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.
    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.
    URI
    toURI()
    Returns a URI equivalent to this URL.

    Methods declared in class Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait
    Modifier and Type
    Method
    Description
    protected Object
    clone()
    Creates and returns a copy of this object.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    Finalization is deprecated and subject to removal in a future release.
    final Class<?>
    getClass()
    Returns the runtime class of this Object.
    final void
    notify()
    Wakes up a single thread that is waiting on this object's monitor.
    final void
    notifyAll()
    Wakes up all threads that are waiting on this object's monitor.
    final void
    wait()
    Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
    final void
    wait(long timeoutMillis)
    Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
    final void
    wait(long timeoutMillis, int nanos)
    Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.