Java Servlet Programming

Chat Server

The daytime server example from the last section demonstrated the nuts and bolts of using each of the three communication techniques for applet-servlet communication. It didn’t take advantage, though, of the persistence gains when using socket communication. Nor did it show off the simplicity of RMI communication or the elegance of RMI callbacks (where the servlet can invoke methods of the applet). It also didn’t provide a compelling reason for why one servlet should support all the communication techniques—there was no state to maintain or complicated code base to collect in one location. So, before we end our discussion of applet-servlet communication, let’s look at a more sophisticated example: a chat server, implemented as a servlet, that supports clients connecting via HTTP, non-HTTP sockets, and RMI.

We’ll build this chat server using all three communication techniques so that it can take advantage of the best, most efficient solution for each client. For example, when the client supports RMI, the servlet can be treated as a remote object, and (where possible) it can treat the applet as a remote object, too. When the client doesn’t support RMI but can support direct socket communication, the chat server can utilize socket persistence and communicate with the client using a non-HTTP socket protocol. And, of course, when all else fails, the chat server can fall back to using HTTP. It would rather not fall back because HTTP, being stateless, requires that the ...