Sockets form the underpinnings of all networking protocols. JDBC, RMI, CORBA, EJB, and the non-Java RPC (Remote Procedure Call), the foundation of the Network File System, or NFS: all of these are implemented by connecting various types of sockets together. Socket connections can be implemented in many languages, not just Java: C, C++, Perl, and Python are also popular, and many others are possible. A client or server written in any one of these languages can communicate with its opposite written in any of the other languages. Therefore, it’s worth taking a quick look at how the ServerSocket behaves, even if you wind up utilizing the higher-level services such as RMI, JDBC, CORBA, or EJB.

The discussion looks first at the ServerSocket itself, then at writing data over a socket in various ways. Finally, there is a complete implementation of a usable network server written in Java: the chat server from the client in the previous chapter.