package TcpExamples; import java.io.*; import java.net.*; /** * Very slightly more complex than example1. A complete copy of example 2. The * only thing this does differently is introduce a loop into the response, so * you don't have to restart the program after one response. Also, it prints out * the socket pair the server sees. Run the program via telnet several times and * compare the socket pairs. * * telnet localhost 2317 * * If you're sophisticated you can contact the instructor's computer while * running this program. * * telnet [ipNumberOfServerLaptop] 2317 * * And have him display the socket pairs he got. * * @author mcgredo */ public class TcpExample3Server { @SuppressWarnings("ConvertToTryWithResources") public static void main(String[] args) { try { // ServerSocket waits for a connection from a client. // Notice that it is outside the loop; ServerSocket // needs to be made only once. System.out.println("TcpExample3Server has really started..."); // it helps debugging to put this on console first ServerSocket serverSocket = new ServerSocket(2317); // Server is up and waiting (i.e. "blocked" or paused) // Loop, infinitely, waiting for client connections. // Stop the program somewhere else. while (true) { Socket clientConnection = serverSocket.accept(); // block until connected to a client // Now hook everything up (i.e. set up the streams), Java style: OutputStream os = clientConnection.getOutputStream(); PrintStream ps = new PrintStream(os); ps.println("This was written by the server"); // this goes back to client! // Print some information locally about the Socket // connection. This includes the port and IP numbers // on both sides (the socket pair.) InetAddress localAddress = clientConnection.getLocalAddress(); InetAddress remoteAddress = clientConnection.getInetAddress(); int localPort = clientConnection.getLocalPort(); int remotePort = clientConnection.getPort(); // My socket pair connection looks like this, to localhost: // Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54876 )) // Socket pair: (( /0:0:0:0:0:0:0:1, 2317 ), ( /0:0:0:0:0:0:0:1, 54881 )) // // Why is the first IP/port the same, while the second set has // different ports? System.out.println("TcpExample3Server socket pair: (( " + localAddress.toString() + ", " + localPort + " ), ( " + remoteAddress.toString() + ", " + remotePort + " ))"); // Notice the use of flush() and close(). Without // the close() to Socket object may stay open for // a while after the client has stopped needing this // connection. Close() explicitly ends the connection. ps.flush(); clientConnection.close(); // like it or not, you're outta here! } } catch (IOException e) { System.out.println("problem with networking"); } } }