Tutorial - Multicast Chat System

/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.com/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved; see license.txt for details.
 */

import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;

public class MulticastChat implements Runnable, WindowListener, ActionListener {
  protected InetAddress group;
  protected int port;

  public MulticastChat (InetAddress group, int port) {
    this.group = group;
    this.port = port;
    initAWT ();
  }

  protected Frame frame;
  protected TextArea output;
  protected TextField input;

  protected void initAWT () {
    frame = new Frame
      ("MulticastChat [" + group.getHostAddress () + ":" + port + "]");
    frame.addWindowListener (this);
    output = new TextArea ();
    output.setEditable (false);
    input = new TextField ();
    input.addActionListener (this);
    frame.setLayout (new BorderLayout ());
    frame.add (output, "Center");
    frame.add (input, "South");
    frame.pack ();
  }

  protected Thread listener;

  public synchronized void start () throws IOException {
    if (listener == null) {
      initNet ();
      listener = new Thread (this);
      listener.start ();
      frame.setVisible (true);
    }
  }

  protected MulticastSocket socket;
  protected DatagramPacket outgoing, incoming;

  protected void initNet () throws IOException {
    socket = new MulticastSocket (port);
    socket.setTimeToLive (5);
    socket.joinGroup (group);
    outgoing = new DatagramPacket (new byte[1], 1, group, port);
    incoming = new DatagramPacket (new byte[65508], 65508);
  }

  public synchronized void stop () throws IOException {
    frame.setVisible (false);
    if (listener != null) {
      listener.interrupt ();
      listener = null;
      try {
        socket.leaveGroup (group);
      } finally {
        socket.close ();
      }
    }
  }

  public void windowOpened (WindowEvent event) {
    input.requestFocus ();
  }

  public void windowClosing (WindowEvent event) {
    try {
      stop ();
    } catch (IOException ex) {
      ex.printStackTrace ();
    }
  }

  public void windowClosed (WindowEvent event) {}
  public void windowIconified (WindowEvent event) {}
  public void windowDeiconified (WindowEvent event) {}
  public void windowActivated (WindowEvent event) {}
  public void windowDeactivated (WindowEvent event) {}

  public void actionPerformed (ActionEvent event) {
    try {
      byte[] utf = event.getActionCommand ().getBytes ("UTF8");
      outgoing.setData (utf);
      outgoing.setLength (utf.length);
      socket.send (outgoing);
      input.setText ("");
    } catch (IOException ex) {
      handleIOException (ex);
    }
  }

  protected synchronized void handleIOException (IOException ex) {
    if (listener != null) {
      output.append (ex + "\n");
      input.setVisible (false);
      frame.validate ();
      if (listener != Thread.currentThread ())
        listener.interrupt ();
      listener = null;
      try {
        socket.leaveGroup (group);
      } catch (IOException ignored) {
      }
      socket.close ();
    }
  }

  public void run () {
    try {
      while (!Thread.interrupted ()) {
        incoming.setLength (incoming.getData ().length);
        socket.receive (incoming);
        String message = new String
          (incoming.getData (), 0, incoming.getLength (), "UTF8");
        output.append (message + "\n");
      }
    } catch (IOException ex) {
      handleIOException (ex);
    }
  }

  public static void main (String[] args) throws IOException {
    if ((args.length != 1) || (args[0].indexOf (":") < 0))
      throw new IllegalArgumentException
        ("Syntax: MulticastChat <group>:<port>");

    int idx = args[0].indexOf (":");
      InetAddress group = InetAddress.getByName (args[0].substring (0, idx));
    int port = Integer.parseInt (args[0].substring (idx + 1));

    MulticastChat chat = new MulticastChat (group, port);
    chat.start ();
  }
}