content: package com.ramaguru.amrita.cys.jpl.net;
  
  import java.io.*;
  import java.net.*;
  
  /**
   * The UDPServer class represents the server side of the UDP client-server application.
   * It listens for client messages and sends responses.
   */
  public class UDPServer {
  
      private static final int PORT = 4424;
      private static final int BUFFER_SIZE = 1024;
  
      /**
       * The main method is the entry point of the server application.
       *
       * @param args command line arguments
       */
      public static void main(String[] args) {
          try {
              // Create a UDP socket
              DatagramSocket serverSocket = new DatagramSocket(PORT);
              System.out.println("Server started. Waiting for clients...");
  
              byte[] receiveBuffer = new byte[BUFFER_SIZE];
  
              while (true) {
                  // Receive client message
                  DatagramPacket receivePacket = new DatagramPacket(receiveBuffer, receiveBuffer.length);
                  serverSocket.receive(receivePacket);
  
                  // Extract client message
                  String clientMessage = new String(receivePacket.getData(), 0, receivePacket.getLength());
                  System.out.println("Received from client: " + clientMessage);
  
                  // Process client message
                  String response = processMessage(clientMessage);
  
                  // Send response to client
                  InetAddress clientAddress = receivePacket.getAddress();
                  int clientPort = receivePacket.getPort();
                  byte[] sendBuffer = response.getBytes();
                  DatagramPacket sendPacket = new DatagramPacket(sendBuffer, sendBuffer.length, clientAddress, clientPort);
                  serverSocket.send(sendPacket);
  
                  System.out.println("Sent to client: " + response);
              }
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  
      /**
       * Processes the client message and generates a response.
       * Modify this method to implement your specific server logic.
       *
       * @param message the client message
       * @return the response to the client
       */
      private static String processMessage(String message) {
          // Placeholder implementation
          return "Server response: " + message.toUpperCase();
      }
  }
  
  