// Fig. 18.7: Client.java
// Client that sends and receives packets to/from a server.
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Client extends JFrame {
   private JTextField enterField;
   private JTextArea displayArea;
   private DatagramSocket socket;

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

      Container container = getContentPane();

      enterField = new JTextField( "Type message here" );
      enterField.addActionListener(
         new ActionListener() { 
            public void actionPerformed( ActionEvent event )
            {
               // create and send packet
               try {
                  displayArea.append( "\nSending packet containing: " +
                     event.getActionCommand() + "\n" );

                  // get message from textfield and convert to byte array
                  String message = event.getActionCommand();
                  byte data[] = message.getBytes();
         
                  // create sendPacket
                  DatagramPacket sendPacket = new DatagramPacket( data, 
                     data.length, InetAddress.getLocalHost(), 5000 );

                  socket.send( sendPacket ); // send packet
                  displayArea.append( "Packet sent\n" );
                  displayArea.setCaretPosition( 
                     displayArea.getText().length() );
               }

               // process problems creating or sending packet
               catch ( IOException ioException ) {
                  displayMessage( ioException.toString() + "\n" );
                  ioException.printStackTrace();
               }

            } // end actionPerformed

         } // end inner class

      ); // end call to addActionListener

      container.add( enterField, BorderLayout.NORTH );

      displayArea = new JTextArea();
      container.add( new JScrollPane( displayArea ),
         BorderLayout.CENTER );

      setSize( 400, 300 );
      setVisible( true );

      // create DatagramSocket for sending and receiving packets
      try {
         socket = new DatagramSocket();
      }

      // catch problems creating DatagramSocket
      catch( SocketException socketException ) {
         socketException.printStackTrace();
         System.exit( 1 );
      }

   } // end Client constructor

   // wait for packets to arrive from Server, display packet contents
   private void waitForPackets()
   {
      while ( true ) { // loop forever

         // receive packet and display contents
         try {

            // set up packet
            byte data[] = new byte[ 100 ];
            DatagramPacket receivePacket = new DatagramPacket( 
               data, data.length );

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

            // display packet contents
            displayMessage( "\nPacket received:" + 
               "\nFrom host: " + receivePacket.getAddress() + 
               "\nHost port: " + receivePacket.getPort() + 
               "\nLength: " + receivePacket.getLength() + 
               "\nContaining:\n\t" + new String( receivePacket.getData(), 
                  0, receivePacket.getLength() ) );
         }
 
         // process problems receiving or displaying packet
         catch( IOException exception ) {
            displayMessage( exception.toString() + "\n" );
            exception.printStackTrace();
         }

      } // end while

   } // end method waitForPackets

   // utility method called from other threads to manipulate 
   // displayArea in the event-dispatch thread
   private void displayMessage( final String messageToDisplay )
   {
      // display message from event-dispatch thread of execution
      SwingUtilities.invokeLater(
         new Runnable() {  // inner class to ensure GUI updates properly

            public void run() // updates displayArea
            {
               displayArea.append( messageToDisplay );
               displayArea.setCaretPosition( 
                  displayArea.getText().length() );
            }

         }  // end inner class

      ); // end call to SwingUtilities.invokeLater
   }

   public static void main( String args[] )
   {
      Client application = new Client();
      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
      application.waitForPackets();
   }

}  // end class Client


/**************************************************************************
 * (C) Copyright 1992-2003 by Deitel & Associates, Inc. and               *
 * Prentice Hall. All Rights Reserved.                                    *
 *                                                                        *
 * DISCLAIMER: The authors and publisher of this book have used their     *
 * best efforts in preparing the book. These efforts include the          *
 * development, research, and testing of the theories and programs        *
 * to determine their effectiveness. The authors and publisher make       *
 * no warranty of any kind, expressed or implied, with regard to these    *
 * programs or to the documentation contained in these books. The authors *
 * and publisher shall not be liable in any event for incidental or       *
 * consequential damages in connection with, or arising out of, the       *
 * furnishing, performance, or use of these programs.                     *
 *************************************************************************/