Java Network Programming, Second Edition

HttpURLConnection

The java.net.HttpURLConnection class is an abstract subclass of URLConnection that provides some additional methods that are helpful when working specifically with http URLs.

public abstract class HttpURLConnection extends URLConnection

In particular, it contains methods to get and set the request method, to decide whether to follow redirects, to get the response code and message, and to figure out whether a proxy server is being used. It also includes several dozen mnemonic constants matching the various HTTP response codes. Finally, it overrides the getPermission( ) method from the URLConnection superclass, though it doesn’t change the semantics of this method at all.

Since this class is abstract and since its only constructor is protected, you can’t directly create instances of HttpURLConnection. However, if you construct a URL object using an http URL, and then invoke its openConnection( ) method, the URLConnection object returned will be an instance of HttpURLConnection. You can cast that URLConnection to HttpURLConnection like this:

URL u = new URL("http://www.amnesty.org/");
URLConnection uc = u.openConnection(  );
HttpURLConnection http = (HttpURLConnection) uc;

Or, skipping a step, like this:

URL u = new URL("http://www.amnesty.org/");
HttpURLConnection http = (HttpURLConnection) u.openConnection(  );

Note

There’s another HttpURLConnection class in the undocumented sun.net.www.protocol.http package. This is a concrete subclass of java.net.HttpURLConnection that ...