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Object | +----java.net.URL
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 Transport 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 file component, even though the
information is not necessarily in a file.
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 an "anchor", also known as a "ref" or a "reference". The anchor is indicated by the sharp sign character "#" followed by more characters. For example,
http://java.sun.com/index.html#chapter1
This anchor 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
FAQ.html
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 anchor is not inherited.
java.net.URL(String, String, int, String)
URL object from the specified
protocol, host, port
number, and file.
java.net.URL(String, String, String)
protocol
name, host name, and file name.
java.net.URL(String)
URL object from the String
representation.
java.net.URL(URL, String)
spec
within a specified context.
equals(Object)
getContent()
getFile()
URL.
getHost()
URL, if applicable.
getPort()
URL.
getProtocol()
URL.
getRef()
URL.
hashCode()
openConnection()
URLConnection object that represents a
connection to the remote object referred to by the URL.
openStream()
URL and returns an
InputStream for reading from that connection.
sameFile(URL)
set(String, String, int, String, String)
setURLStreamHandlerFactory(URLStreamHandlerFactory)
URLStreamHandlerFactory.
toExternalForm()
URL.
toString()
URL.
URL
public URL(String protocol,
String host,
int port,
String file) throws MalformedURLException
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.
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:
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.
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.handler.protol.pkgs
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
URLStreamHandler, then the next package
in the list is tried.
sun.net.www.protocol.<protocol>.Handler
URLStreamHandler, then a
MalformedURLException is thrown.
URL
public URL(String protocol,
String host,
String file) throws MalformedURLException
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.
URL
public URL(String spec) throws MalformedURLException
URL object from the String
representation.
This constructor is equivalent to a call to the two-argument
constructor with a null first argument.
String to parse as a URL.
URL
public URL(URL context,
String spec) throws MalformedURLException
spec
within a specified context. If the context argument
is not null and the spec argument is a
partial URL specification, then any of the strings missing
components are inherited from the context argument.
The specification given by the String argument is
parsed to determine if it specifies a protocol. If the
String contains an ASCII colon ':'
character before the first occurrence of an ASCII slash character
'/', then the characters before the colon comprise
the protocol.
spec argument does not specify a protocol:
null, then the
protocol is copied from the context argument.
null, then a
MalformedURLException is thrown.
spec argument does specify a protocol:
null, or specifies a
different protocol than the specification argument, the context
argument is ignored.
null and specifies
the same protocol as the specification, the host,
port number, and file are copied from
the context argument into the newly created URL.
The constructor then searches for an appropriate stream protocol
handler of type URLStreamHandler as outlined for:
java.net.URL#URL(java.lang.String, java.lang.String, int,
java.lang.String)
parseURL method is called to parse the remaining
fields of the specification that override any defaults set by the
context argument.
String representation of a URL.
equals
public boolean equals(Object obj)
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 on
the host. The anchors of the URL objects are not compared.
This method is equivalent to:
(obj instanceof URL) && sameFile((URL)obj)
true if the objects are the same;
false otherwise.
getContent
public final java.lang.Object getContent() throws IOException
openConnection().getContent()
getFile
public java.lang.String getFile()
URL.
URL.
getHost
public java.lang.String getHost()
URL, if applicable.
For "file" protocol, this is an empty string.
URL.
getPort
public int getPort()
URL.
Returns -1 if the port is not set.
getProtocol
public java.lang.String getProtocol()
URL.
URL.
getRef
public java.lang.String getRef()
URL.
URL.
hashCode
public int hashCode()
URL.
openConnection
public java.net.URLConnection openConnection() throws IOException
URLConnection object that represents a
connection to the remote object referred to by the URL.
If there is not already an open connection, the connection is
opened by calling the openConnection method of the
protocol handler for this URL.
URLConnection to the URL.
openStream
public final java.io.InputStream openStream() throws IOException
URL and returns an
InputStream for reading from that connection. This
method is a shorthand for:
openConnection().getInputStream()
sameFile
public boolean sameFile(URL other)
true if this URL and the
other argument both refer to the same resource.
The two URLs might not both contain the same anchor.
URL to compare against.
true if they reference the same remote object;
false otherwise.
set
protected void set(String protocol,
String host,
int port,
String file,
String ref)
setURLStreamHandlerFactory
public static synchronized void setURLStreamHandlerFactory(URLStreamHandlerFactory fac)
URLStreamHandlerFactory.
This method can be called at most once by an application.
The URLStreamHandlerFactory instance is used to
construct a stream protocol handler from a protocol name.
toExternalForm
public java.lang.String toExternalForm()
URL. The
string is created by calling the toExternalForm
method of the stream protocol handler for this object.
toString
public java.lang.String toString()
URL. The
string is created by calling the toExternalForm
method of the stream protocol handler for this object.
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