Chapter 30.   Network Chat

Three versions of a network chat application are developed in this chapter.

1. Threaded TCP Clients and Server.
   The server uses threads to communicate with its clients, and a shared object to maintain client information. Each client employs a thread to watch for server communications (typically copies of other users' messages).
    
2. UDP Multicasting Clients and a Name Server.
   The clients send messages to each other via UDP multicasting. However, a client wishing to join the chat group must first communicate with a name server which sends it the group address (or rejects the request). A departing client must notify the name server, so that it can maintain a current list of participants. A client wanting a list of other users sends a message to the server, rather than querying the group.
    
3. Clients using a Servlet as a Server.
   The clients communicate with a chat servlet, sending messages as arguments of the servlet's URL. The servlet maintains client information, which is shared between the multiple threads executing inside the servlet instance. Each client has a separate thread which periodically queries the servlet for any new messages.

These examples illustrate the features of client/server models, peer-to-peer, and HTTP tunneling respectively, mechanisms first introduced in Chapter 29.

Downloads

• The PDF file for the draft chapter (the old ch.19) (239 KB). Last updated: 24th June 2003.
  
• Zipped Source code (27 KB). Last updated: 20th April 2005. The book's code.
  

• Up to the Killer Game Programming in Java Index Page
• Back to Chapter 29. Networking Basics
• On to Chapter 31. A Networked Two-Person Game