Java Network Programming, Second Edition

Accessing Password-Protected Sites

Many popular sites, such as The Wall Street Journal, require a username and password for access. Some sites, such as Oracle TechNet, implement this through HTTP authentication. Others, such as the Java Developer Connection, implement it through cookies and HTML forms. Java’s URL class can access sites that use HTTP authentication, though you’ll of course need to tell it what username and password to use. Java does not provide support for sites that use nonstandard, cookie-based authentication, partially because Java doesn’t really support cookies and partially because this requires parsing and submitting HTML forms. You can provide this support yourself using the URLConnection class to read and write the HTTP headers where cookies are set and returned. However, doing so is decidedly nontrivial, and often requires custom code for each site you want to connect to. It’s really hard to do short of implementing a complete web browser with full HTML forms and cookie support. Accessing sites protected by standard, HTTP authentication is much easier.

The Authenticator Class

Starting in Java 1.2 (but not available in Java 1.1), the java.net package includes an Authenticator class you can use to provide a username and password for sites that protect themselves using HTTP authentication:

public abstract class Authenticator extends Object

Since Authenticator is an abstract class, you must subclass it. Different subclasses may retrieve the information ...