client.java

用UDP协议实现两台电脑间的相互对话通信

// Fig 17.5 Client.java
// Set up a Client that will read information sent
// from a Server and display the information.
   
// Java core packages
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;
 
// Java extension packages
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;
// initialize chatServer and set up GUI
      public Client( String host )
      {
         super( "Client" );
   
         // set server to which this client connects
         chatServer = host;
   
         Container container = getContentPane();
   
         // create enterField and register listener
         enterField = new JTextField();
         enterField.setEnabled( false );
         enterField.addActionListener(new ActionListener() 
	{
                  // send message to server
               public void actionPerformed( ActionEvent event )
               {
                  sendData( event.getActionCommand() );
               }
   
            }  // end anonymous inner class
   
         ); // end call to addActionListener
  
         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
      public void runClient() 
      {
         // connect to server, get streams, process connection
         try {
  
           // Step 1: Create a Socket to make connection
            connectToServer();
  
            // Step 2: Get the input and output streams
            getStreams();
  
           // Step 3: Process connection
            processConnection();
   
           // Step 4: Close connection
          closeConnection();
        }
  
         // server closed connection
         catch ( EOFException eofException ) {
            System.out.println( "Server terminated connection" );
        }
// process problems communicating with server
         catch ( IOException ioException ) {
            ioException.printStackTrace();
         }
      }
   
     // get streams to send and receive data
     private void getStreams() throws IOException
     {
       // set up output stream for objects
         output = new ObjectOutputStream(client.getOutputStream() );
   
         // flush output buffer to send header information
      output.flush();
  
     // set up input stream for objects
        input = new ObjectInputStream(client.getInputStream() );
  
        displayArea.append( "\nGot I/O streams\n" );
     }
// connect to server
     private void connectToServer() throws IOException
     {      
        displayArea.setText( "Attempting connection\n" );
  
        // create Socket to make connection to server
        client = new Socket(InetAddress.getByName(chatServer),6000);
  
        // display connection information
        displayArea.append( "Connected to: " +client.getInetAddress().getHostName());
     }
  
     // process connection with server

     private void processConnection() throws IOException
     {
        // enable enterField so client user can send messages
        enterField.setEnabled( true );
// process messages sent from server
        do {
  
          // read message and display it
           try {
          message = ( String ) input.readObject();
              displayArea.append( "\n" + message );
              displayArea.setCaretPosition(displayArea.getText().length());
          }
  
          // catch problems reading from server
           catch ( ClassNotFoundException classNotFoundException ) {
              displayArea.append( "\nUnknown object type received" );
          }
  
        } while ( !message.equals( "SERVER>>> TERMINATE" ) );
  
    }  // end method process connection
    // close streams and socket
     private void closeConnection() throws IOException
     {
        displayArea.append( "\nClosing connection" );
        output.close();
       input.close();
       client.close();
     }
 
     // send message to server
     private void sendData( String message )
     {
        // send object to server
        try {
          output.writeObject( "CLIENT>>> " + message );
           output.flush();
        displayArea.append( "\nCLIENT>>>" + message );
       }
  
        // process problems sending object
        catch ( IOException ioException ) {
           displayArea.append( "\nError writing object" );
        }
     }
// execute application
    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();
     }
  
  }  // end class Client