server.java

用UDP协议实现两台电脑间的相互对话通信

// Fig 17.4 Server.java
// Set up a Server that will receive a connection
// from a client, send a string to the client,
// and close the connection.

// Java core packages
import java.io.*;
import java.net.*;
import java.awt.*;
import java.awt.event.*;

// Java extension packages
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.setEnabled( false );
   
        enterField.addActionListener(new ActionListener() 
            {
   
               // send message to client
               public void actionPerformed( ActionEvent e )
              {
                  sendData(e.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 );
      }
   
      // 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(6000,100);
  
            while ( true ) 
            {
   
              // Step 2: Wait for a connection.
               waitForConnection();
   
              // Step 3: Get input and output streams.
               getStreams();
   
               // Step 4: Process connection.
              processConnection();
   
               // Step 5: Close connection.
               closeConnection();
   
               ++counter;
            }
         }
// process EOFException when client closes connection 
         catch ( EOFException eofException )
         {
            System.out.println( "Client terminated connection" );
         }
  
         // process problems with I/O
        catch ( IOException ioException ) 
        {
            ioException.printStackTrace();
        }
      }
   
     // wait for connection to arrive, then display connection info
     private void waitForConnection() throws IOException
    {
        displayArea.setText( "Waiting for connection\n" );
  
        // allow server to accept a connection
       connection = server.accept();
             
       displayArea.append( "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() );
 
        // flush output buffer to send header information
       output.flush();
  
        // set up input stream for objects
        input = new ObjectInputStream(Connection.getInputStream() );
  
        displayArea.append( "\nGot I/O streams\n" );
     }
  
     // process connection with client
     
     private void processConnection() throws IOException
     {
        // send connection successful message to client
        String message = "SERVER>>> Connection successful";
	output.writeObject( message );
        output.flush();
  
        // enable enterField so server user can send messages
        enterField.setEnabled( true );
  
        // process messages sent from client
        do {
  
           // read message and display it
           try {
              message = ( String ) input.readObject();
              displayArea.append( "\n" + message );
              displayArea.setCaretPosition(displayArea.getText().length() );
           }
  
           // catch problems reading from client
           catch ( ClassNotFoundException classNotFoundException )
            {
              displayArea.append( "\nUnknown object type received" );
           }
  
       } while ( !message.equals( "CLIENT>>> TERMINATE" ) );
 }
  
     // close streams and socket
     private void closeConnection() throws IOException
     {
        displayArea.append( "\nUser terminated connection" );
        enterField.setEnabled( false );
        output.close();
        input.close();
        connection.close();
     }
// send message to client
     private void sendData( String message )
     {
        // send object to client
        try {
           output.writeObject( "SERVER>>> " + message );
           output.flush();
           displayArea.append( "\nSERVER>>>" + message );
        }
  
        // process problems sending object
        catch ( IOException ioException ) {
           displayArea.append( "\nError writing object" );
        }
     }
// execute application
     public static void main( String args[] )
     {
        Server application = new Server();
  
        application.setDefaultCloseOperation(
           JFrame.EXIT_ON_CLOSE );
  
        application.runServer();
     }
  
  }  // end class Server