// Fig. 24.9: Server.java
// Server that receives and sends packets from/to a client.
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.awt.BorderLayout;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class Server extends JFrame 
{
   private JTextArea displayArea; // displays packets received
   private DatagramSocket socket; // socket to connect to client

   // set up GUI and DatagramSocket
   public Server()
   {
      super( "Server" );

      displayArea = new JTextArea(); // create displayArea
      add( new JScrollPane( displayArea ), BorderLayout.CENTER );
      setSize( 400, 300 ); // set size of window
      setVisible( true ); // show window

      try // create DatagramSocket for sending and receiving packets
      {
         socket = new DatagramSocket( 5000 );
      } // end try
      catch ( SocketException socketException ) 
      {
         socketException.printStackTrace();
         System.exit( 1 );
      } // end catch
   } // end Server constructor

   // wait for packets to arrive, display data and echo packet to client
   public void waitForPackets()
   {
      while ( true ) 
      {
         try // receive packet, display contents, return copy to client
         {
            byte data[] = new byte[ 100 ]; // set up packet
            DatagramPacket receivePacket = 
               new DatagramPacket( data, data.length );

            socket.receive( receivePacket ); // wait to receive packet

            // display information from received packet 
            displayMessage( "\nPacket received:" + 
               "\nFrom host: " + receivePacket.getAddress() + 
               "\nHost port: " + receivePacket.getPort() + 
               "\nLength: " + receivePacket.getLength() + 
               "\nContaining:\n\t" + new String( receivePacket.getData(), 
                  0, receivePacket.getLength() ) );

            sendPacketToClient( receivePacket ); // send packet to client
         } // end try
         catch ( IOException ioException )
         {
            displayMessage( ioException.toString() + "\n" );
            ioException.printStackTrace();
         } // end catch
      } // end while
   } // end method waitForPackets

   // echo packet to client
   private void sendPacketToClient( DatagramPacket receivePacket ) 
      throws IOException
   {
      displayMessage( "\n\nEcho data to client..." );

      // create packet to send
      DatagramPacket sendPacket = new DatagramPacket( 
         receivePacket.getData(), receivePacket.getLength(), 
         receivePacket.getAddress(), receivePacket.getPort() );

      socket.send( sendPacket ); // send packet to client
      displayMessage( "Packet sent\n" );
   } // end method sendPacketToClient

   // manipulates displayArea in the event-dispatch thread
   private void displayMessage( final String messageToDisplay )
   {
      SwingUtilities.invokeLater(
         new Runnable() 
         {
            public void run() // updates displayArea
            {
               displayArea.append( messageToDisplay ); // display message
            } // end method run
         } // end anonymous inner class
      ); // end call to SwingUtilities.invokeLater
   } // end method displayMessage
} // end class Server

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 * (C) Copyright 1992-2005 by Deitel & Associates, Inc. and               *
 * Pearson Education, Inc. All Rights Reserved.                           *
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