Swing application with network event handling

Question

Hello, hope this is the right place for this post. I'm the design phase of a client application in java which talks to a remote server written in C via sockets. I have a design problem: I want my Swing app to have a GUI with buttons and all for normal activities, which activities report to the server, and I want the client to react to server calls anytime without interrupting normal GUi activities. Plus, all must work together, so I would prefer having a single thread for the app. (Think of an IRC client: the user uses the GUI for activities and sendim messages, and meanwhile the client listens for messages from the server and display them as they arrive). My question is: is this possible?
I have something like (in pseudo-java):
classMyApp extends JFrame {
  public MyApp() {
    // Manages and create the GUI
    NetHandler h = new NetHandler(this);
    h.connect();
    while(true) {
      h.pollNetEvents();
class NetHandler {
  private BufferedReader iStream;
  private PrintWriter oStream;
  private MyApp app;
  public NetHandler(MyApp a) {
    app = a;
    Socket socket = createSocket(ip, port);
    iStream = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    oStream = new PrintWriter(socket.getOutputStream());
    handshakeWithServer(); // Login & Password
  public pollNetEvents() {
    try {
      String s;
      for (;;) {
        s = iStream.readLine();
        if (s.equals("") == false)
          break;
        else
          app.parseCommand(s);
    catch (IOException e) {
      app.sendMessage("Error in pollNetEvent: " + e);
}Roughly, something like this. With this solution the GUI works, but I cannot get the message the server sends.
I hope my message is clear enough. Can anybody help me with the design of my app? Thanks a lot.
Fabio.

Answer 1

You might consider posting this in the Swing forum. You might get a more complete response there, but here are my first thoughts.
-- I think you will end up wanting to use multiple threads, but only one thread will update the UI. For more about threading in Swing, see this tutorial: http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html
and maybe also here: http://www.sourcebeat.com/TitleAction.do?id=10 (look at the sample chapter on Threads)
-- For the polling code ...
Of course, if you use the classes provided for client/server communication described below, you don't need to write your own polling code. You may still wish worry about threading so that your UI remains responsive and does not encounter major issues: http://java.sun.com/developer/JDCTechTips/2005/tt0419.html#1
-- Updates to the UI from thread(s) that are not on the Event Dispatch Thread (the one that controls the UI) must be posted using the SwingUtilities methods, such as invokeLater
Message was edited by:
pthorson