Server.java

// Fig. 18.4: Server.java
// Set up a Server that will receive a connection from a client, send
// a string to the client, and close the connection.
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Server extends JFrame {
   private JTextField enterField;
   private JTextArea displayArea;
   private ObjectOutputStream output;
   private ObjectInputStream input;
   private ServerSocket server;
   private Socket connection;
   private int counter = 1;

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

      Container container = getContentPane();

      // create enterField and register listener
      enterField = new JTextField();
      enterField.setEditable( false );
      enterField.addActionListener(
         new ActionListener() {

            // send message to client
            public void actionPerformed( ActionEvent event )
            {
               sendData( event.getActionCommand() );
               enterField.setText( "" );
            }
         }
      );

      container.add( enterField, BorderLayout.NORTH );

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

      setSize( 300, 150 );
      setVisible( true );

   } // end Server constructor

   // set up and run server
   public void runServer()
   {
      // set up server to receive connections; process connections
      try {

         // Step 1: Create a ServerSocket.
         server = new ServerSocket( 12345, 100 );

         while ( true ) {

            try {
               waitForConnection(); // Step 2: Wait for a connection.
               getStreams();        // Step 3: Get input & output streams.
               processConnection(); // Step 4: Process connection.
            }

            // process EOFException when client closes connection
            catch ( EOFException eofException ) {
               System.err.println( "Server terminated connection" );
            }

            finally {
               closeConnection();   // Step 5: Close connection.
               ++counter;
            }

         } // end while

      } // end try

      // process problems with I/O
      catch ( IOException ioException ) {
         ioException.printStackTrace();
      }

   } // end method runServer

   // wait for connection to arrive, then display connection info
   private void waitForConnection() throws IOException
   {
      displayMessage( "Waiting for connection\n" );
      connection = server.accept(); // allow server to accept connection
      displayMessage( "Connection " + counter + " received from: " +
         connection.getInetAddress().getHostName() );
   }

   // get streams to send and receive data
   private void getStreams() throws IOException
   {
      // set up output stream for objects
      output = new ObjectOutputStream( connection.getOutputStream() );
      output.flush(); // flush output buffer to send header information

      // set up input stream for objects
      input = new ObjectInputStream( connection.getInputStream() );

      displayMessage( "\nGot I/O streams\n" );
   }

   // process connection with client
   private void processConnection() throws IOException
   {
      // send connection successful message to client
      String message = "Connection successful";
      sendData( message );

      // enable enterField so server user can send messages
      setTextFieldEditable( true );

      do { // process messages sent from client

         // read message and display it
         try {
            message = ( String ) input.readObject();
            displayMessage( "\n" + message );
         }

         // catch problems reading from client
         catch ( ClassNotFoundException classNotFoundException ) {
            displayMessage( "\nUnknown object type received" );
         }

      } while ( !message.equals( "CLIENT>>> TERMINATE" ) );

   } // end method processConnection

   // close streams and socket
   private void closeConnection()
   {
      displayMessage( "\nTerminating connection\n" );
      setTextFieldEditable( false ); // disable enterField

      try {
         output.close();
         input.close();
         connection.close();
      }
      catch( IOException ioException ) {
         ioException.printStackTrace();
      }
   }

   // send message to client
   private void sendData( String message )
   {
      // send object to client
      try {
         output.writeObject( "SERVER>>> " + message );
         output.flush();
         displayMessage( "\nSERVER>>> " + message );
      }

      // process problems sending object
      catch ( IOException ioException ) {
         displayArea.append( "\nError writing object" );
      }
   }

   // 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
   }

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

            public void run()  // sets enterField's editability
            {
               enterField.setEditable( editable );
            }

         }  // end inner class

      ); // end call to SwingUtilities.invokeLater
   }

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

}  // end class Server

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