The class

The class represents a URL. There are constructors to create new URLs and methods to parse the different parts of a URL. However the heart of the class are the methods that allow you to get an InputStream from a URL so you can read data from a server.

The URL class is closely tied to protocol and content handlers. The objective is to separate the data being downloaded from the the protocol used to download it. The protocol handler is responsible for communicating with the server, that is moving bytes from the server to the client. It handles any necessary negotiation with the server and any headers. Its job is to return only the actual bytes of the data or file requested. The content handler takes those bytes and translates them into some kind of Java object such as an InputStream or ImageProducer.

When you construct a URL object, Java looks for a protocol handler that understands the protocol part of the URL such as "http" or "mailto". If no such handler is found, the constructor throws a MalformedURLException. The exact protocols that are supported vary from implementation to implementation though http and file are supported pretty much everywhere. Sun's JDK 1.1 understands ten:

The last five are custom protocols defined by Sun and used internally by the JDK and HotJava.

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Copyright 1997, 1999 Elliotte Rusty Harold
Last Modified August 4