PDAP Public Review Draft

java.net
Class URL

java.lang.Object
  |
  +--java.net.URL

public final class URL
extends java.lang.Object

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.ncsa.uiuc.edu/demoweb/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.ncsa.uiuc.edu. The information on that host machine is named /demoweb/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.ncsa.uiuc.edu:8080/demoweb/url-primer.html
 

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.

 
 CDLC AWT Support Building Block:
 This class is subsetted to only represent the URL as a location specification.
 All links to the J2SE IO model for controlling URL connections has been removed
 since J2ME and CLDC use a very different IO model.  In the CLDC context, this class
 is used to verify, contstruct, and decontruct URL strings.
 Classes removed include:
    - URL(java.lang.String protocol, java.lang.String host, int port, java.lang.String file, java.net.URLStreamHandler handler) 
    - URL(URL context, java.lang.String spec, java.net.URLStreamHandler handler)
    - getContent()
    - getContent(java.lang.Class[] classes)
    - openConnection()
    - openStream()
    - setURLStreamHandlerFactory()
 
 

Since:
JDK1.0

Constructor Summary
URL(java.lang.String spec)
          Creates a URL object from the String representation.
URL(java.lang.String protocol, java.lang.String host, int port, java.lang.String file)
          Creates a URL object from the specified protocol, host, port number, and file.
URL(java.lang.String protocol, java.lang.String host, java.lang.String file)
          Creates a URL from the specified protocol name, host name, and file name.
URL(URL context, java.lang.String spec)
          Creates a URL by parsing the given spec within a specified context.
 
Method Summary
 boolean equals(java.lang.Object obj)
          Compares two URLs.
 java.lang.String getAuthority()
          Returns the authority part of this URL.
 java.lang.String getFile()
          Returns the file name of this URL.
 java.lang.String getHost()
          Returns the host name of this URL, if applicable.
 java.lang.String getPath()
          Returns the path part of this URL.
 int getPort()
          Returns the port number of this URL.
 java.lang.String getProtocol()
          Returns the protocol name of this URL.
 java.lang.String getQuery()
          Returns the query part of this URL.
 java.lang.String getRef()
          Returns the anchor (also known as the "reference") of this URL.
 java.lang.String getUserInfo()
          Returns the userInfo part of this URL.
 int hashCode()
          Creates an integer suitable for hash table indexing.
 boolean sameFile(URL other)
          Compares two URLs, excluding the "ref" fields.
protected  void set(java.lang.String protocol, java.lang.String host, int port, java.lang.String file, java.lang.String ref)
          Sets the fields of the URL.
protected  void set(java.lang.String protocol, java.lang.String host, int port, java.lang.String authority, java.lang.String userInfo, java.lang.String path, java.lang.String query, java.lang.String ref)
          Sets the specified 8 fields of the URL.
 java.lang.String toExternalForm()
          Constructs a string representation of this URL.
 java.lang.String toString()
          Constructs a string representation of this URL.
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

URL

public URL(java.lang.String protocol,
           java.lang.String host,
           int port,
           java.lang.String file)
    throws MalformedURLException
Creates a URL object from the specified protocol, host, port number, and file. Specifying a port number of -1 indicates that the URL should use the default port for the protocol.

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.

URL

public URL(java.lang.String protocol,
           java.lang.String host,
           java.lang.String file)
    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.

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)

URL

public URL(java.lang.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 the string specifies an unknown protocol.
See Also:
URL(java.net.URL, java.lang.String)

URL

public URL(URL context,
           java.lang.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 any 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. 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.
See Also:
URL(java.lang.String, java.lang.String, int, java.lang.String)
Method Detail

set

protected void set(java.lang.String protocol,
                   java.lang.String host,
                   int port,
                   java.lang.String file,
                   java.lang.String ref)
Sets the fields of the URL.
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

set

protected void set(java.lang.String protocol,
                   java.lang.String host,
                   int port,
                   java.lang.String authority,
                   java.lang.String userInfo,
                   java.lang.String path,
                   java.lang.String query,
                   java.lang.String ref)
Sets the specified 8 fields of the URL.
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

getQuery

public java.lang.String getQuery()
Returns the query part of this URL.
Returns:
the query part of this URL.

getPath

public java.lang.String getPath()
Returns the path part of this URL.
Returns:
the path part of this URL.

getUserInfo

public java.lang.String getUserInfo()
Returns the userInfo part of this URL.
Returns:
the userInfo part of this URL.

getAuthority

public java.lang.String getAuthority()
Returns the authority part of this URL.
Returns:
the authority part of this URL.

getPort

public int getPort()
Returns the port number of this URL. Returns -1 if the port is not set.
Returns:
the port number

getProtocol

public java.lang.String getProtocol()
Returns the protocol name of this URL.
Returns:
the protocol of this URL.

getHost

public java.lang.String getHost()
Returns the host name of this URL, if applicable.
Returns:
the host name of this URL.

getFile

public java.lang.String getFile()
Returns the file name of this URL.
Returns:
the file name of this URL.

getRef

public java.lang.String getRef()
Returns the anchor (also known as the "reference") of this URL.
Returns:
the anchor (also known as the "reference") of this URL.

equals

public boolean equals(java.lang.Object obj)
Compares two URLs. The result is true if and only if the argument is not null and is a URL object that represents the same URL as this object. Two URL objects are equal if they have the same protocol and reference the same host, the same port number on the host, and the same file and anchor on the host.
Overrides:
equals in class java.lang.Object
Parameters:
obj - the URL to compare against.
Returns:
true if the objects are the same; false otherwise.

hashCode

public int hashCode()
Creates an integer suitable for hash table indexing.
Overrides:
hashCode in class java.lang.Object
Returns:
a hash code for this URL.

sameFile

public boolean sameFile(URL other)
Compares two URLs, excluding the "ref" fields. Returns true if this URL and the other argument both refer to the same resource. The two URLs might not both contain the same anchor.
Parameters:
other - the URL to compare against.
Returns:
true if they reference the same remote object; false otherwise.

toString

public java.lang.String toString()
Constructs a string representation of this URL.
Overrides:
toString in class java.lang.Object
Returns:
a string representation of this object.
See Also:
URL(java.lang.String, java.lang.String, int, java.lang.String)

toExternalForm

public java.lang.String toExternalForm()
Constructs a string representation of this URL.
Returns:
a string representation of this object.
See Also:
URL(java.lang.String, java.lang.String, int, java.lang.String)

PDAP 1.0 Spec, Rev. 0.16