import java.net.*; 
import java.io.*; 
public class UDPServer{
    public static void main(String args[]){
	DatagramSocket aSocket = null;
	try{
            aSocket = new DatagramSocket(6789); 
	    byte[] buffer = new byte[1000]; 
	    while(true){
                DatagramPacket request = new DatagramPacket(buffer, buffer.length); 
		aSocket.receive(request); 
		DatagramPacket reply = new DatagramPacket(request.getData(), 
                 request.getLength(), request.getAddress(), request.getPort());
		aSocket.send(reply);  
            }
        }
        catch (SocketException e){
            System.out.println("Socket: " + e.getMessage()); 
        }
        catch (IOException e) {
            System.out.println("IO: " + e.getMessage());
        }
	finally{ if(aSocket != null) aSocket.close();}
    }
}