URL: http://download.oracle.com/javase/tutorial/rmi/compiling.html

In the middle of the page:

The network accessibility of the class files enables the RMI runtime to download code when needed. Rather than defining its own protocol for code downloading, RMI uses URL protocols supported by the Java platform (for example, HTTP) to download code. Note that using a full, heavyweight web server to serve these class files is unnecessary. For example, a simple HTTP server that provides the functionality needed to make classes available for downloading in RMI through HTTP can be found at http://java.sun.com/javase/technologies/core/basic/rmi/class-server.zip.

The class-server.zip is not reachable.