How to handle multiple clients with DatagramSocket

Question

I am trying to handle multiple clients with 1 datagramSocket bind to one port (basically I have only one port to use, and I can not use TCP or any other ports). At the server side I have two threads one for receiving packets and buffering them, another for processing the packets in the buffer and sending replies.
I can have multiple clients sending datagramPackets to me and I will have to process the packets and send them to DIFFERENT clients. Ex. Client 1 sends datagramPacket to Server which sends the processed packet to Client 2. Also Client 2 sends a datagramPacket to Server which again processes the packet and sends it to Client1. May have Client 3 and 4 doing the same thing at the same time... and so on...
My root class is creating the datagramSocket(somePort) and two threads (receiver and sender). How can I use the socket that I created in these two threads??
I have done the following and I am getting "java.net.bindexception". When I am sending stuff from Client1 to Client2 everything is fine but when I start sending something from Client2 to Client 1, I get the bindexception... Client 1 is using port 3000, Client 2 is using port 4000.
I really don't have a lot of experience in socket programming so I am not sure if there is a much simpler way to do this. I appreciate all the tips and help that I can get...
Thanks...
class UDP_serv
     static DatagramSocket udpSocket;
     final static int SERVER_PORT     = 2000;
     public static void main(String[] args) throws SocketException
          udpSocket= new DatagramSocket(SERVER_PORT);
          new DataReceiver().start ();
          new DataSender().start ();
     static class DataReceiver extends Thread
          DataReceiver()
               Thread.currentThread().setName("DataReceiver");
          public void run()
               while (true)
                    byte pckt[] = new byte [MaxMsgSize];          
                    DatagramPacket dp = new DatagramPacket (pckt, pckt.length);
                    try
                         udpSocket.receive (dp);
                         //PUSH TO RECEIVE BUFFER
                    catch(Exception e)
                         e.printStackTrace();
     static class DataSender extends Thread
          DataSender()
               Thread.currentThread().setName("DataSender");
          public void run()
               while (true)
                    processDataMsg();
      static void processDataMsg() 
         DatagramPacket op;
         InetAddress DA = null;
         int DP = 0;
         byte [] outPacket = null;
         // POP FROM RECEIVE BUFFER
         // SOME PROCESSING HERE     
         // Set Destination Address (DA)
         // Set Destination Port (DP)
         // DA and DP are the forwarding IP and Port addresses
         // not the addresses original packet was sent from.
         try
          op = new DatagramPacket (outPacket, outPacket.length,DA, DP);
          udpSocket.send(op);
         catch (IOException e)
          e.printStackTrace();
}Also for development and testing purposes, I am running the two clients and the server on the same machine (windows xp-32b) so all of the Destination IP Addresses are 127.0.0.1. and as I said Ports that I am using are 2000, 3000, 4000 (Server, Client1, Client2).

Answer 1

Hmm I have minimized the code and it seems to be working now.
I think I have an error in the header portion of the data I am sending, where I am storing the source IP/Port and destination IP/Port. I think the server in the middle is messing these values up while sending them to the destination Client. Because the destination client actually receives the stuff and sends the reply back to the server, but the reply packet's headers has 0/0 as the dest IP / Port...
Server is giving me java.net.BindException: Cannot assign requested address error when it tries to forward the reply it received from the client2 as the address it is trying to send is 0!
I guess it doesnt just give this error when you try to open two sockets to the same port...
Paul, Thanks for the direction on how to proceed... took me a while get the minimized code but at least figured out the problem. Well still have to make sure that is THE problem though :)
As far as the statics goes how can I change those to non static ones? Where do I make an instance of the top level class that creates the threads? and how do I pass the DatagramSocket to the threads/ if I dont need to pass how do I call or use the datagramSocket I created in the top level class? I mean do I still kinda have it like a global variable on the top?? A very simple example would be much appreciated...
I think these might be really basic questions but I am having a rough time with the hierarchy in java...