How to send a packet to multiple recipients?

Question

I'm writing a small chat program in java. What I have so far for the server, is this:
import java.io.*;
public class datagramServer {
     public static void main(String[] args) throws IOException {
          new datagramServerThread().start();
}datagramServerThread class:
import java.net.*;
import java.util.*;
import java.io.*;
public class datagramServerThread extends Thread {
    protected DatagramSocket socket = null;
    boolean listening = true;
    datagramProtocol DGP = new datagramProtocol();
    public datagramServerThread() throws IOException {
     this("datagramServerThread");
    public datagramServerThread(String name) throws IOException {
        super(name);
        socket = new DatagramSocket(4445);
    public void run() {
        while (listening) {
            try {
                byte[] buf = new byte[256];
                DatagramPacket packet = new DatagramPacket(buf, buf.length);
                socket.receive(packet);
                String processSendBack = new String(packet.getData());
                String sendBack = DGP.processInput(processSendBack);
                buf = sendBack.getBytes();
                InetAddress address = packet.getAddress();
                int port = packet.getPort();
                packet = new DatagramPacket(buf, buf.length, address, port);
                socket.send(packet);
            catch (IOException e) {
                e.printStackTrace();
        socket.close();
}And the datagramProtocol class:
import java.io.*;
import java.net.*;
public class datagramProtocol {
     String output;
     public String processInput(String toProcess) {
          output = toProcess;
          return output;
}Pretty simple, and it works great, if you just want to chat with yourself... ;)
The client is really simple, just sends and receives, nothing fancy.
What I want to know, is how would I send anything any client sends, to every other connected client?
btw, I was wondering if it's good coding practice to put everything into a seperate class like that. I probably could've put everything into one, but it's a little neater in seperate files.
Thanks,
Alex

Answer 1

Can a publish/subscribe sort of model be used in it's
place? Or how about just a listener model rather
than pushing each request? This way the clients just
register themselves and listeners and you merely
propogate an event. There would be no need to keep
track of each IP, etc.
Just thinking out loud here... :)Well, as I understand, on a publish/subscriber model, the publisher has to keep some sort of reference to the listener in order to send the events when they happen.
Keeping the sockets to the clients seems to me as good as a reference can be on a TCP/IP connection short of using RMI to do that, but if the client/server must be decoupled from the language what I sugested is a publish/subscriber model. The clients are the subscribers, they ad themselves as such upon connecting to the server, the server wich is the publisher store their reference as subscribers by keeping the socket where they agreed upon communicating.
When the publisher has a new message to be published it walks the list of references giving them the event, wich is the message posted.
Sure it could be done with events just notifying the arrival of new messages but it would just complicate the model beyond the need. For the client would have to wait for the event and them send a request asking for the actual message, in order to do such a system he would have to create a simple protocol of comunication between the client and the server.
May the code be with you.