Module java.base
Package java.net

Class URL

java.lang.Object
java.net.URL
All Implemented Interfaces:
Serializable
public final classURLextendsObjectimplementsSerializable
ClassURL 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 ishttp (HyperText Transfer Protocol) and that the information resides on a host machine namedwww.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 thepath 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 forhttp is80. An alternative port could be specified as:

     http://www.example.com:1080/docs/resource1.html

The syntax ofURL is defined byRFC 2396: Uniform Resource Identifiers (URI): Generic Syntax, amended byRFC 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 describedhere.

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 tagchapter1 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 ofURL

Thejava.net.URL constructors are deprecated. Developers are encouraged to usejava.net.URI to parse or construct aURL. 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 callingURI.parseServerAuthority() to validate that the authority component can be parsed as a server-based authority, and then callingURI.toURL() to create theURL instance.

The URL constructors are specified to throwMalformedURLException but the actual parsing/validation that is performed is implementation dependent. Some parsing/validation may be delayed until later, when the underlyingstream handler's implementation is called. Being able to construct an instance ofURL 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, theURI class does perform escaping of its component fields in certain circumstances. The recommended way to manage the encoding and decoding of URLs is to useURI, and to convert between these two classes usingtoURI() andURI.toURL().

TheURLEncoder andURLDecoder 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. ThePath.of(URI) factory method and theFile(URI) constructor can be used to createPath orFile objects from a file URI.Path.toUri() andFile.toURI() can be used to create aURI from a file path, which can be converted to URL usingURI.toURL(). Applications should never try toconstruct orparse aURL from the direct string representation of aFile orPath instance.

Before constructing aURL from aURI, and depending on the protocol involved, applications should consider validating whether the URI authoritycan be parsed as server-based.

Some components of a URL or URI, such asuserinfo, may be abused to construct misleading URLs or URIs. Applications that deal with URLs or URIs should take into account the recommendations advised inRFC3986, Section 7, Security Considerations.

AllURL constructors may throwMalformedURLException. In particular, if the underlyingURLStreamHandler implementation rejects, or is known to reject, any of the parameters,MalformedURLException may be thrown. Typically, a constructor that calls the stream handler'sparseURL method may throwMalformedURLException if the underlying stream handler implementation of that method throwsIllegalArgumentException. 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: