Java Server Development with java.net

java.net.ServerSocket is a class for implementing server sockets. ServerSockets can be created unbound, or bound to a particular port. In either case, the constructor may throw an IOException, which may be thrown when attempting to open the socket. The most important method on a server socket is accept(), which listens for a connection to be made to the socket and accepts it. Example code (notice the interplay between the ServerSocket and Socket classes):

import java.net.ServerSocket;
import java.net.BindException;

ServerSocket listenSocket = null;
try {
listenSocket = new ServerSocket(serverPort);
while(true) {
// listen for and accept incoming connection
Socket clientSocket = listenSocket.accept();
// do something
}
} catch (BindException bindEx) {
// error message to say server is already running on serverPort
System.exit(0);
}

The socket class abstracts the concept of an endpoint of communication between two machines. A nice visual analogy of the socket idiom is the probe-and-drogue method of aerial refuelling used by the USAF. Pictures can be seen on aerospaceweb.

SSLServerSocket is a special instance of ServerSocket; these sockets aer generally created by an SSLServerSocketFactory.