Java in a Nutshell, 5th Edition

Name

URLConnection

Synopsis

This abstract class defines a network connection to an object specified by a URL. URL.openConnection( ) returns a URLConnection instance. You should use a URLConnection object when you want more control over the downloading of data than is available through the simpler URL methods. connect( ) actually establishes the network connection. Some methods must be called before the connection is made, and others depend on being connected. The methods that depend on being connected call connect( ) themselves if no connection exists yet, so you never need to call this method explicitly. The getContent( ) methods are just like the same-named methods of the URL class: they download the data referred to by the URL and parse it into an appropriate type of object (such as a string or an image). In Java 1.3 and later, there is a version of getContent( ) that allows you to specify the types of parsed objects that you are willing to accept by passing an array of Class objects. If you prefer to parse the URL content yourself instead of calling getContent( ), you can call getInputStream( ) (and getOutputStream( ) if the URL protocol supports writing) to obtain a stream through which you can read (or write) data from (or to) the resource identified by the URL.

Before a connection is established, you may want to set request fields (such as HTTP request headers) to refine the URL request. Use setRequestProperty( ) to set a new value for a named header. In Java 1.4 and later, ...