UDP Клиентский серверный мост

Question

Задача - отправить сообщение с клиента на сервер через мост и ответить с сервера клиенту через мост.

Я выполнил первую часть, но не смог выполнить второй шаг, то есть ответ сервера клиенту через мост.

клиент может отправить первое сообщение на сервер черезмост создан, но после достижения сервера сервер должен ответить обратно с измененным кодом, который не работает.

будут полезны любые предложения или указания относительно подхода к цели.

Заранее спасибо

мой код

Клиент

import java.io.*;
import java.net.*;

class UDPClient
{
public static void main(String args[]) throws Exception
{

   //getting input from the user and sending to Bridge
  BufferedReader inFromUser =
     new BufferedReader(new InputStreamReader(System.in));
  DatagramSocket clientSocket = new DatagramSocket();
  InetAddress IPAddress = InetAddress.getByName("localhost");
  byte[] sendData = new byte[1024];
  byte[] receiveData = new byte[1024];
  String sentence = inFromUser.readLine();


  sendData = sentence.getBytes();
  DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 4000);
  clientSocket.send(sendPacket);

  //Getting data from the Bridge
  DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
  clientSocket.receive(receivePacket);
  String modifiedSentence = new String(receivePacket.getData());
  System.out.println("C: FROM SERVER:" + modifiedSentence);
  clientSocket.close();
}
}

Сервер

    import java.io.*;
import java.net.*;

class UDPServer
{
   public static void main(String args[]) throws Exception
      {
         DatagramSocket serverSocket = new DatagramSocket(5000);
            byte[] receiveData = new byte[1024];
            byte[] sendData = new byte[1024];

            while(true)
               {
                   //receiveing data from the bridge
                  DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
                  serverSocket.receive(receivePacket);
                  String sentence = new String( receivePacket.getData());
                  System.out.println("S:RECEIVED: " + sentence);

                  InetAddress IPAddress = InetAddress.getByName("localhost");


                  // Sending data to the bridge
                  int port = 4000;
                  String capitalizedSentence = sentence.toUpperCase();
                  sendData = capitalizedSentence.getBytes();
                  DatagramPacket sendPacket =
                  new DatagramPacket(sendData, sendData.length, IPAddress, port);
                  serverSocket.send(sendPacket);
               }
      }
   }

Мост

 import java.io.*;
import java.net.*;

/**
 * Write a description of class Bridge here.
 *
 * @author (your name)
 * @version (a version number or a date)
 */
public class Bridge
{
   public static void main(String args[]) throws Exception{

       DatagramSocket bridgeSocket1 = new DatagramSocket(4000);
       DatagramSocket bridgeSocket2 = new DatagramSocket();

       byte[] receiveData = new byte[1024];
       byte[] sendData = new byte[1024];

       DatagramPacket  receivePacket;
       DatagramPacket  sendPacket;
       InetAddress  IPAddress = InetAddress.getByName("localhost");


       while(true){

           //Receiveing data from the UDPClient
           receivePacket = new DatagramPacket(receiveData, receiveData.length);
           bridgeSocket1.receive(receivePacket);  


           //Sending data to UDPServer
           String sentence = new String(receivePacket.getData());
           System.out.println("B: Data Received:" + sentence); 
           int port = 5000;
           sendData = sentence.getBytes();
           sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);
           bridgeSocket2.send(sendPacket);


           // Receiving Data from the UDPServer
           receivePacket = new DatagramPacket(receiveData,receiveData.length);
           bridgeSocket1.receive(receivePacket);


           String capitalizedSentence = new String(receivePacket.getData());
           System.out.println("Capitalized Sentence in the Bridge Class: " + capitalizedSentence);


           //Sending data to the UDPClient

           sendData = capitalizedSentence.getBytes();
           sendPacket = new DatagramPacket(sendData,sendData.length,IPAddress,5000);
           bridgeSocket2.send(sendPacket);
        }
        }
    }