import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class EchoServer {
	
	static final int PORT = 8000;
	static final int MAX_DATAGRAM_SIZE = 65536;
	
	public static void main(String[] args) throws Exception {

		// create in/out UDP socket
		try (DatagramSocket socket = new DatagramSocket( PORT )) {
		   for(;;) { // server endless loop
		      // prepare an empty datagram
		      byte[] buffer = new byte[MAX_DATAGRAM_SIZE];
		      DatagramPacket echoRequest = new DatagramPacket( buffer, buffer.length );
		      // wait for an incoming datagram
		      socket.receive( echoRequest );

		      //get UDP datagram payload
		      byte[] echoRequestData = echoRequest.getData();
		      int echoRequestLength = echoRequest.getLength();
		      System.out.println( "GOT: "+ new String( echoRequestData, 0, echoRequestLength));  
		        
		      // prepare an UDP datagram with the reply
		      DatagramPacket echoReply = new DatagramPacket( echoRequestData, echoRequestLength ) ;
		      // as well as destination IP address and port
		      echoReply.setAddress( echoRequest.getAddress() );
		      echoReply.setPort( echoRequest.getPort() );
		      
		      //send reply
		      socket.send( echoReply );
		    }    
		} // socket.close()
	}

}