client.java

this file contains java source code to connect two computers in a network

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 ObjectOutputStream output;
    private ObjectInputStream input;
    private String message = "";
    private String chatServer;
    private Socket client;

   
   public Client( String host )
   {
          super( "Client" );

         chatServer = host;
         Container container = getContentPane();
         enterField = new JTextField();
         enterField.setEditable( false );
         enterField.addActionListener (
                 new ActionListener()
                 {

               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 );

   } 

   // connect to server and process messages from server
   private void runClient() 
   {
       try 
         {
              connectToServer();        
              getStreams();                 
              processConnection();    
        }

      catch ( EOFException eofException ) 
      {
         System.err.println( "Client terminated connection" );
      }

      
      catch ( IOException ioException ) 
      {
         ioException.printStackTrace();
      }

      finally 
      {
         closeConnection(); 
      }

   } 

   // connect to server
   private void connectToServer() throws IOException
   {      
      displayMessage( "Attempting connection\n" );

    client = new Socket( InetAddress.getByName( chatServer ), 12345 );

  displayMessage( "Connected to: " +client.getInetAddress().getHostName() );
   }

   // get streams to send and receive data
   private void getStreams() throws IOException
    {
      
          output = new ObjectOutputStream( client.getOutputStream() );      
         
          input = new ObjectInputStream( client.getInputStream() );
    }

   // process connection with server
   private void processConnection() throws IOException
   {
         setTextFieldEditable( true );
        do
         { 
             // read message and display it
                try
                 {
                        message = ( String ) input.readObject();
                        displayMessage( "\n" + message );
                }
              catch ( ClassNotFoundException classNotFoundException ) 
                {
                      displayMessage( "\nUnknown object type received" );
                }
        }
        while ( !message.equals( "SERVER>>> TERMINATE" ) );

   } 
   
   // close streams and socket
   private void closeConnection() 
   {
        displayMessage( "\nClosing connection" );
        setTextFieldEditable( false ); 
         try 
         {
              output.close();
              input.close();
              client.close();
         }
        catch( IOException ioException ) 
        {
             ioException.printStackTrace();
        }
   }

   // send message to server
   private void sendData( String message )
   {
      try 
      {
         output.writeObject( "CLIENT>>> " + message );
         output.flush();
         displayMessage( "\nCLIENT>>> " + message );
      }
      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 )
   {
      SwingUtilities.invokeLater
      (
             new Runnable() 
              {  
                      public void run() 
                      {
           displayArea.append( messageToDisplay );
           displayArea.setCaretPosition( displayArea.getText().length() );
                      }
            } 
      ); 
   }

   private void setTextFieldEditable( final boolean editable )
   {
           SwingUtilities.invokeLater
           (
                       new Runnable()
                        {  
                               public void run() 
                                {
        enterField.setEditable( editable );
                                }
                       }  
            ); 
   }

   public static void main( String args[] )
   {
      Client application;

      if ( args.length == 0 )
         application = new Client( "127.0.0.1" );
      else
         application = new Client( args[ 0 ] );

      application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
      application.runClient();
   }
}