servletlistclient.java

JAVA网络编程技术内幕一书的源代码

/*
 * Java Network Programming, Second Edition
 * Merlin Hughes, Michael Shoffner, Derek Hamner
 * Manning Publications Company; ISBN 188477749X
 *
 * http://nitric.com/jnp/
 *
 * Copyright (c) 1997-1999 Merlin Hughes, Michael Shoffner, Derek Hamner;
 * all rights reserved; see license.txt for details.
 */

import java.io.*;
import java.net.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class ServletListClient implements DistributedList, Runnable {
  public static final int UPDATE_PERIOD = 10 * 1000;

  protected URL servlet;
  protected IDList idList;
  
  public ServletListClient (URL servlet) {
    try {
      this.servlet = new URL (servlet, servlet.getFile () + '/');
    } catch (MalformedURLException ignored) {
    }
    idList = new IDList ();
  }

  protected Thread updater;
  
  public synchronized void start ()
    throws IOException, ClassNotFoundException {
    if (updater == null) {
      getUpdate ();
      updater = new Thread (this);
      updater.start ();
    }
  }

  public synchronized void stop () {
    Thread updater = this.updater;
    this.updater = null;
    if (updater != null)
      updater.interrupt ();
  }

  public void run () {
    Thread myself = Thread.currentThread ();
    try {
      while (updater == myself) {
        Thread.sleep (UPDATE_PERIOD);
        getUpdate ();
      }
    } catch (InterruptedException ignored) {
    } catch (IOException ex) {
      ex.printStackTrace ();
    } catch (ClassNotFoundException ex) {
      ex.printStackTrace ();
    } finally {
      updater = null;
    }
  }

  protected synchronized void getUpdate () throws IOException, ClassNotFoundException {
    int count = idList.getUpdateCount ();
    URL url = new URL (servlet, "getUpdate?count=" + count);
    URLConnection conn = url.openConnection ();
    conn.setUseCaches (false);
    ObjectInputStream in = new ObjectInputStream (conn.getInputStream ());
    IDList newList = (IDList) in.readObject ();
    in.close ();
    if (newList != null) {
      idList = newList;
      fireChangeEvent (new ChangeEvent (this));
    }
  }

  public synchronized void addElement (Object element) {
    try {
      URL url = new URL (servlet, "addElement");
      URLConnection conn = url.openConnection ();
      conn.setRequestProperty ("Content-type", "application/octet-stream");
      conn.setDoOutput (true);
      ObjectOutputStream out = new ObjectOutputStream (
        conn.getOutputStream ());
      out.writeObject (element);
      out.close ();
      ObjectInputStream in = new ObjectInputStream (
        conn.getInputStream ());
      ID id = (ID) in.readObject ();
      in.close ();
      if (id != null) {
        idList.addElement (id, element);
        fireChangeEvent (new ChangeEvent (this));
      }
    } catch (IOException ex) {
      ex.printStackTrace ();
    } catch (ClassNotFoundException ex) {
      ex.printStackTrace ();
    }
  }

  public synchronized void updateElement (Object oldElement, Object newElement) {
    ID id = idList.getID (oldElement);
    if (id != null) {
      try {
        URL url = new URL (servlet, "updateElement");
        URLConnection conn = url.openConnection ();
        conn.setDoOutput (true);
        ObjectOutputStream out = new ObjectOutputStream (
          conn.getOutputStream ());
        out.writeObject (id);
        out.writeObject (newElement);
        out.close ();
        ObjectInputStream in = new ObjectInputStream (
          conn.getInputStream ());
        ID newID = (ID) in.readObject ();
        in.close ();
        if (newID != null) {
          idList.updateElement (id, newID, newElement);
          fireChangeEvent (new ChangeEvent (this));
        }
      } catch (IOException ex) {
        ex.printStackTrace ();
      } catch (ClassNotFoundException ex) {
        ex.printStackTrace ();
      }
    }
  }

  public synchronized void replaceElement (Object oldElement, Object newElement) {
    ID id = idList.getID (oldElement);
    if (id != null) {
      try {
        URL url = new URL (servlet, "replaceElement");
        URLConnection conn = url.openConnection ();
        conn.setDoOutput (true);
        ObjectOutputStream out = new ObjectOutputStream (
          conn.getOutputStream ());
        out.writeObject (id);
        out.writeObject (newElement);
        out.close ();
        ObjectInputStream in = new ObjectInputStream (
          conn.getInputStream ());
        ID newID = (ID) in.readObject ();
        in.close ();
        if (newID != null) {
          idList.replaceElement (id, newID, newElement);
          fireChangeEvent (new ChangeEvent (this));
        }
      } catch (IOException ex) {
        ex.printStackTrace ();
      } catch (ClassNotFoundException ex) {
        ex.printStackTrace ();
      }
    }
  }

  public synchronized void removeElement (Object element) {
    ID id = idList.getID (element);
    if (id != null) {
      try {
        URL url = new URL (servlet, "removeElement");
        URLConnection conn = url.openConnection ();
        conn.setDoOutput (true);
        ObjectOutputStream out = new ObjectOutputStream (
          conn.getOutputStream ());
        out.writeObject (id);
        out.close ();
        ObjectInputStream in = new ObjectInputStream (
          conn.getInputStream ());
        boolean okay = in.readBoolean ();
        in.close ();
        if (okay) {
          idList.removeElement (id);
          fireChangeEvent (new ChangeEvent (this));
        }
      } catch (IOException ex) {
        ex.printStackTrace ();
      }
    }
  }

  public Enumeration getElements () {
    return idList.getElements ();
  }

  protected Vector listeners = new Vector ();
  
  public void addChangeListener (ChangeListener listener) {
    listeners.addElement (listener);
  }

  public void removeChangeListener (ChangeListener listener) {
    listeners.removeElement (listener);
  }

  protected void fireChangeEvent (ChangeEvent changeEvent) {
    synchronized (listeners) {
      for (int i = 0; i < listeners.size (); ++ i)
        ((ChangeListener) listeners.elementAt (i)).changeOccurred (changeEvent);
    }
  }
}