This framework provides a quite simple way to implement message based client-server communication. It assumes that you have a fairly solid knowledge on C/S and Java programming.
The framework shows how you can implement socket-based communication and use the Java object serialisation mechanisms to send Java-objects from a server to a client.
If you are only interested in message based c/s communication (and not in technical details), you should probably try the Java Message Service (JMS) API. An example is also available from this website.
The package is available as a zipped tar file: jcs-2.13.tgz (51 Kb).