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URL

public final class URL
extends Object implements Serializable

java.lang.Object
   ↳ java.net.URL


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:

http://www.socs.uts.edu.au/MosaicDocs-old/url-primer.html

In general, a URL can be broken into several parts. The previous example of a URL indicates that the protocol to use is http (HyperText Transfer Protocol) and that the information resides on a host machine named www.socs.uts.edu.au. The information on that host machine is named /MosaicDocs-old/url-primer.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.socs.uts.edu.au:80/MosaicDocs-old/url-primer.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 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.

Summary

Public constructors

URL(String protocol, String host, int port, String file)

Creates a URL object from the specified protocol, host, port number, and file.

URL(String protocol, String host, String file)

Creates a URL from the specified protocol name, host name, and file name.

URL(String protocol, String host, int port, String file, URLStreamHandler handler)

Creates a URL object from the specified protocol, host, port number, file, and handler.

URL(String spec)

Creates a URL object from the String representation.

URL(URL context, String spec)

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

URL(URL context, String spec, URLStreamHandler handler)

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

Public methods

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.

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.

URLConnection openConnection()

Returns a URLConnection instance that represents a connection to the remote object referred to by the URL.

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.

Protected methods

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.

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

Sets the fields of the URL.

Inherited methods

From class java.lang.Object

Public constructors

URL

Added in API level 1
URL (String protocol, 
                String host, 
                int port, 
                String file)

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:

  1. 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.
  2. 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.
  3. 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 String: the name of the protocol to use.
host String: the name of the host.
port int: the port number on the host.
file String: the file on the host
Throws
MalformedURLException if an unknown protocol is specified.

See also:

URL

Added in API level 1
URL (String protocol, 
                String host, 
                String file)

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 String: the name of the protocol to use.
host String: the name of the host.
file String: the file on the host.
Throws
MalformedURLException if an unknown protocol is specified.

See also:

URL

Added in API level 1
URL (String protocol, 
                String host, 
                int port, 
                String file, 
                URLStreamHandler handler)

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 of null indicates that the URL should use a default stream handler for the protocol, as outlined for: 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 String: the name of the protocol to use.
host String: the name of the host.
port int: the port number on the host.
file String: the file on the host
handler URLStreamHandler: 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:

URL

Added in API level 1
URL (String spec)

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 String: 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

Added in API level 1
URL (URL context, 
                String spec)

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 URL: the context in which to parse the specification.
spec String: 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

Added in API level 1
URL (URL context, 
                String spec, 
                URLStreamHandler handler)

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 URL: the context in which to parse the specification.
spec String: the String to parse as a URL.
handler URLStreamHandler: 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:

Public methods

equals

Added in API level 1
boolean equals (Object obj)

Compares this URL for equality with another object.

If the given object is not a URL then this method immediately returns false.

Two URL objects are equal if they have the same protocol, reference equivalent hosts, have the same port number on the host, and the same file and fragment of the file.

Returns true if this URL equals o. URLs are equal if they have the same protocol, host, port, file, and reference.

Network I/O Warning

Some implementations of URL.equals() resolve host names over the network. This is problematic:

  • The network may be slow. Many classes, including core collections like Map and Set expect that equals and hashCode will return quickly. By violating this assumption, this method posed potential performance problems.
  • Equal IP addresses do not imply equal content. Virtual hosting permits unrelated sites to share an IP address. This method could report two otherwise unrelated URLs to be equal because they're hosted on the same server.
  • The network may not be available. Two URLs could be equal when a network is available and unequal otherwise.
  • The network may change. The IP address for a given host name varies by network and over time. This is problematic for mobile devices. Two URLs could be equal on some networks and unequal on others.

This problem is fixed in Android 4.0 (Ice Cream Sandwich). In that release, URLs are only equal if their host names are equal (ignoring case).

Parameters
obj Object: the URL to compare against.
Returns
boolean true if the objects are the same; false otherwise.

getAuthority

Added in API level 1
String getAuthority ()

Gets the authority part of this URL.

Returns
String the authority part of this URL

getContent

Added in API level 1
Object getContent ()

Gets the contents of this URL. This method is a shorthand for:

     openConnection().getContent()
 

Returns
Object the contents of this URL.
Throws
IOException if an I/O exception occurs.

See also:

getContent

Added in API level 1
Object getContent (Class[] classes)

Gets the contents of this URL. This method is a shorthand for:

     openConnection().getContent(Class[])
 

Parameters
classes Class: an array of Java types
Returns
Object the content object of this URL that is the first match of the types specified in the classes array. null if none of the requested types are supported.
Throws
IOException if an I/O exception occurs.

See also:

getDefaultPort

Added in API level 1
int getDefaultPort ()

Gets the default port number of the protocol associated with this URL. If the URL scheme or the URLStreamHandler for the URL do not define a default port number, then -1 is returned.

Returns
int the port number

getFile

Added in API level 1
String getFile ()

Gets the file name of this URL. The returned file portion will be the same as getPath(), plus the concatenation of the value of getQuery(), if any. If there is no query portion, this method and getPath() will return identical results.

Returns
String the file name of this URL, or an empty string if one does not exist

getHost

Added in API level 1
String getHost ()

Gets the host name of this URL, if applicable. The format of the host conforms to RFC 2732, i.e. for a literal IPv6 address, this method will return the IPv6 address enclosed in square brackets ('[' and ']').

Returns
String the host name of this URL.

getPath

Added in API level 1
String getPath ()

Gets the path part of this URL.

Returns
String the path part of this URL, or an empty string if one does not exist

getPort

Added in API level 1
int getPort ()

Gets the port number of this URL.

Returns
int the port number, or -1 if the port is not set

getProtocol

Added in API level 1
String getProtocol ()

Gets the protocol name of this URL.

Returns
String the protocol of this URL.

getQuery

Added in API level 1
String getQuery ()

Gets the query part of this URL.

Returns
String the query part of this URL, or null if one does not exist

getRef

Added in API level 1
String getRef ()

Gets the anchor (also known as the "reference") of this URL.

Returns
String the anchor (also known as the "reference") of this URL, or null if one does not exist

getUserInfo

Added in API level 1
String getUserInfo ()

Gets the userInfo part of this URL.

Returns
String the userInfo part of this URL, or null if one does not exist

hashCode

Added in API level 1
int hashCode ()

Creates an integer suitable for hash table indexing.

The hash code is based upon all the URL components relevant for URL comparison. As such, this operation is a blocking operation.

Returns
int a hash code for this URL.

openConnection

Added in API level 1
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. Invoking this method preempts the system's default ProxySelector settings.

Parameters
proxy Proxy: the Proxy through which this connection will be made. If direct connection is desired, Proxy.NO_PROXY should be specified.
Returns
URLConnection a URLConnection to the URL.
Throws
IOException if an I/O exception occurs.
SecurityException if a security manager is present and the caller doesn't have permission to connect to the proxy.
IllegalArgumentException will be thrown if proxy is null, or proxy has the wrong type
UnsupportedOperationException if the subclass that implements the protocol handler doesn't support this method.

See also:

openConnection

Added in API level 1
URLConnection openConnection ()

Returns a URLConnection instance that represents a connection to the remote object referred to by the URL.

A new instance of URLConnection is created every time when invoking the URLStreamHandler.openConnection(URL) method of the protocol handler for this URL.

It should be noted that a URLConnection instance does not establish the actual network connection on creation. This will happen only when calling URLConnection.connect().

If for the URL's protocol (such as HTTP or JAR), there exists a public, specialized URLConnection subclass belonging to one of the following packages or one of their subpackages: java.lang, java.io, java.util, java.net, the connection returned will be of that subclass. For example, for HTTP an HttpURLConnection will be returned, and for JAR a JarURLConnection will be returned.

Returns
URLConnection a URLConnection linking to the URL.
Throws
IOException if an I/O exception occurs.

See also:

openStream

Added in API level 1
InputStream openStream ()

Opens a connection to this URL and returns an InputStream for reading from that connection. This method is a shorthand for:

     openConnection().getInputStream()
 

Returns
InputStream an input stream for reading from the URL connection.
Throws
IOException if an I/O exception occurs.

See also:

sameFile

Added in API level 1
boolean sameFile (URL other)

Compares two URLs, excluding the fragment component.

Returns true if this URL and the other argument are equal without taking the fragment component into consideration.

Parameters
other URL: the URL to compare against.
Returns
boolean true if they reference the same remote object; false otherwise.

setURLStreamHandlerFactory

Added in API level 1
void setURLStreamHandlerFactory (URLStreamHandlerFactory fac)

Sets an application's URLStreamHandlerFactory. This method can be called at most once in a given Java Virtual Machine.

The URLStreamHandlerFactory instance is used to construct a stream protocol handler from a protocol name.

If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException.

Parameters
fac URLStreamHandlerFactory: the desired factory.
Throws
Error if the application has already set a factory.
SecurityException if a security manager exists and its checkSetFactory method doesn't allow the operation.

See also:

toExternalForm

Added in API level 1
String toExternalForm ()

Constructs a string representation of this URL. The string is created by calling the toExternalForm method of the stream protocol handler for this object.

Returns
String a string representation of this object.

See also:

toString

Added in API level 1
String toString ()

Constructs a string representation of this URL. The string is created by calling the toExternalForm method of the stream protocol handler for this object.

Returns
String a string representation of this object.

See also:

toURI

Added in API level 1
URI toURI ()

Returns a URI equivalent to this URL. This method functions in the same way as new URI (this.toString()).

Note, any URL instance that complies with RFC 2396 can be converted to a URI. However, some URLs that are not strictly in compliance can not be converted to a URI.

Returns
URI a URI instance equivalent to this URL.
Throws
URISyntaxException if this URL is not formatted strictly according to to RFC2396 and cannot be converted to a URI.

Protected methods

set

Added in API level 1
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. This is not a public method so that only URLStreamHandlers can modify URL fields. URLs are otherwise constant.

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

set

Added in API level 1
void set (String protocol, 
                String host, 
                int port, 
                String file, 
                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 String: the name of the protocol to use
host String: the name of the host
port int: the port number on the host
file String: the file on the host
ref String: the internal reference in the URL
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