Chapter 7. URLConnections
URLConnection is an abstract class that represents an active connection to a resource specified by a URL. The
URLConnection class has two different but related purposes. First, it provides more control over the interaction with a server (especially an HTTP server) than the
URL class. A
URLConnection can inspect the header sent by the server and respond accordingly. It can set the header fields used in the client request. Finally, a
URLConnection can send data back to a web server with
PUT, and other HTTP request methods. We will explore all of these techniques in this chapter.
URLConnection class is part of Java’s protocol handler mechanism, which also includes the
URLStreamHandler class. The idea behind protocol handlers is simple: they separate the details of processing a protocol from processing particular data types, providing user interfaces, and doing the other work that a monolithic web browser performs. The base
java.net.URLConnection class is abstract; to implement a specific protocol, you write a subclass. These subclasses can be loaded at runtime by applications. For example, if the browser runs across a URL with a strange scheme, such as compress, rather than throwing up its hands and issuing an error message, it can download a protocol handler for this unknown protocol and use it to communicate with the server.
URLConnection classes are present in the
java.net package. The concrete subclasses are hidden inside ...