abstractclient.java

java版的简单聊天室程序

// This file contains material supporting section 3.7 of the textbook:
// "Object Oriented Software Engineering" and is issued under the open-source
// license found at www.lloseng.com 

package ocsf;

import java.io.*;
import java.net.*;


/**
* The <code> AbstractClient </code> contains all the
* methods necessary to set up the client side of a client-server
* architecture.  When a client is thus connected to the
* server, the two programs can then exchange <code> Object </code>
* instances.<p>
*
* Method <code> handleMessageFromServer </code> must be defined by
* a concrete subclass. Several other hook methods may also be
* overriden.<p>
*
* Several public service methods are provided to
* application that use this framework.<p>
*
* Project Name: OCSF (Object Client-Server Framework)<p>
*
* @author Dr. Robert Lagani&egrave;re
* @author Dr. Timothy C. Lethbridge
* @author Fran&ccedil;ois  B&eacutel;langer
* @author Paul Holden
* @version February 2001 (2.12)
*/
public abstract class AbstractClient implements Runnable
{

// INSTANCE VARIABLES ***********************************************

  /**
  * Sockets are used in the operating system as channels
  * of communication between two processes.
  * @see java.net.Socket
  */
  private Socket clientSocket;

  /**
  * The stream to handle data going to the server.
  */
  private ObjectOutputStream output;

  /**
  * The stream to handle data from the server.
  */
  private ObjectInputStream input;

  /**
  * The thread created to read data from the server.
  */
  private Thread clientReader;

  /**
  * Indicates if the thread is ready to stop.
  * Needed so that the loop in the run method knows when to stop
  * waiting for incoming messages.
  */
  private boolean readyToStop= false;

  /**
  * The server's host name.
  */
  private String host;

  /**
  * The port number.
  */
  private int port;

// CONSTRUCTORS *****************************************************

  /**
   * Constructs the client.
   *
   * @param  host  the server's host name.
   * @param  port  the port number.
   */
  public AbstractClient(String host, int port)
  {
    // Initialize variables
    this.host = host;
    this.port = port;
  }

// INSTANCE METHODS *************************************************

  /**
   * Opens the connection with the server.
   * If the connection is already opened, this call has no effect.
   *
   * @exception IOException if an I/O error occurs when opening.
   */
  final public void openConnection() throws IOException
  {
    // Do not do anything if the connection is already open
    if(isConnected())
      return;

    //Create the sockets and the data streams
    try
    {
      clientSocket= new Socket(host, port);
      output = new ObjectOutputStream(clientSocket.getOutputStream());
      input = new ObjectInputStream(clientSocket.getInputStream());
    }
    catch (IOException ex)
    // All three of the above must be closed when there is a failure
    // to create any of them
    {
      try
      {
        closeAll();
      }
      catch (Exception exc) { }

      throw ex; // Rethrow the exception.
    }

    clientReader = new Thread(this);  //Create the data reader thread
    readyToStop = false;
    clientReader.start();  //Start the thread
  }

  /**
   * Sends an object to the server. This is the only way that
   * methods should communicate with the server.
   *
   * @param msg   The message to be sent.
   * @exception IOException if an I/O error occurs when sending
   */
  final public void sendToServer(Object msg) throws IOException
  {
    if (clientSocket == null || output == null)
      throw new SocketException("socket does not exist");

    output.writeObject(msg);
  }

  /**
   * Closes the connection to the server.
   *
   * @exception IOException if an I/O error occurs when closing.
   */
  final public void closeConnection() throws IOException
  {
    // Prevent the thread from looping any more
    readyToStop= true;

    try
    {
      closeAll();
    }
    finally
    {
      // Call the hook method
      connectionClosed();
    }
  }

// ACCESSING METHODS ------------------------------------------------

  /**
   * @return true if the client is connnected.
   */
  final public boolean isConnected()
  {
    return clientReader!=null && clientReader.isAlive();
  }

  /**
   * @return the port number.
   */
  final public int getPort()
  {
    return port;
  }

  /**
   * Sets the server port number for the next connection.
   * The change in port only takes effect at the time of the
   * next call to openConnection().
   *
   * @param port the port number.
   */
  final public void setPort(int port)
  {
    this.port = port;
  }

  /**
   * @return the host name.
   */
  final public String getHost()
  {
    return host;
  }

  /**
   * Sets the server host for the next connection.
   * The change in host only takes effect at the time of the
   * next call to openConnection().
   *
   * @param host the host name.
   */
  final public void setHost(String host)
  {
    this.host = host;
  }

  /**
   * returns the client's description.
   *
   * @return the client's Inet address.
   */
  final public InetAddress getInetAddress()
  {
    return clientSocket.getInetAddress();
  }

// RUN METHOD -------------------------------------------------------

  /**
   * Waits for messages from the server. When each arrives,
   * a call is made to <code>handleMessageFromServer()</code>.
   * Not to be explicitly called.
   */
  final public void run()
  {
    connectionEstablished();

    // The message from the server
    Object msg;

    // Loop waiting for data

    try
    {
      while(!readyToStop)
      {
        // Get data from Server and send it to the handler
        // The thread waits indefinitely at the following
        // statement until something is received from the server
        msg = input.readObject();

        // Concrete subclasses do what they want with the
        // msg by implementing the following method
        handleMessageFromServer(msg);
      }
    }
    catch (Exception exception)
    {
      if(!readyToStop)
      {
        try
        {
          closeAll();
        }
        catch (Exception ex) { }

        connectionException(exception);
      }
    }
    finally
    {
      clientReader = null;
    }
  }

// METHODS DESIGNED TO BE OVERRIDDEN BY CONCRETE SUBCLASSES ---------

  /**
   * Hook method called after the connection has been closed.
   * The default implementation does nothing. The method
   * may be overriden by subclasses to perform special processing
   * such as cleaning up and terminating, or attempting to
   * reconnect.
   */
  protected void connectionClosed() {}

  /**
   * Hook method called each time an exception is thrown by the
   * client's thread that is waiting for messages from the server.
   * The method may be overridden by subclasses.
   *
   * @param exception the exception raised.
   */
  protected void connectionException(Exception exception) {}

  /**
   * Hook method called after a connection has been established.
   * The default implementation does nothing.
   * It may be overridden by subclasses to do anything they wish.
   */
  protected void connectionEstablished() {}

  /**
   * Handles a message sent from the server to this client.
   * This MUST be implemented by subclasses, who should respond to
   * messages.
   *
   * @param msg   the message sent.
   */
  protected abstract void handleMessageFromServer(Object msg);


// METHODS TO BE USED FROM WITHIN THE FRAMEWORK ONLY ----------------

  /**
   * Closes all aspects of the connection to the server.
   *
   * @exception IOException if an I/O error occurs when closing.
   */
  private void closeAll() throws IOException
  {
    try
    {
      //Close the socket
      if (clientSocket != null)
        clientSocket.close();

      //Close the output stream
      if (output != null)
        output.close();

      //Close the input stream
      if (input != null)
        input.close();
    }
    finally
    {
      // Set the streams and the sockets to NULL no matter what
      // Doing so allows, but does not require, any finalizers
      // of these objects to reclaim system resources if and
      // when they are garbage collected.
      output = null;
      input = null;
      clientSocket = null;
    }
  }
}
// end of AbstractClient class