SwingWorker


1   /*
2    * $Id: SwingWorker.java,v 1.1.1.1 2004/06/16 01:43:39 davidson1 Exp $
3    *
4    * Copyright 2004 Sun Microsystems, Inc., 4150 Network Circle,
5    * Santa Clara, California 95054, U.S.A. All rights reserved.
6    */
7   
8   package org.jdesktop.swing.utils;
9   
10  import javax.swing.SwingUtilities  ;
11  
12  /**
13   * This is the 3rd version of SwingWorker (also known as
14   * SwingWorker 3), an abstract class that you subclass to
15   * perform GUI-related work in a dedicated thread.  For
16   * instructions on using this class, see:
17   * 
18   * http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html
19   *
20   * Note that the API changed slightly in the 3rd version:
21   * You must now invoke start() on the SwingWorker after
22   * creating it.
23   */
24  public abstract class SwingWorker {
25      private Object   value;  // see getValue(), setValue()
26      private Thread   thread;
27  
28      /** 
29       * Class to maintain reference to current worker thread
30       * under separate synchronization control.
31       */
32      private static class ThreadVar {
33          private Thread   thread;
34          ThreadVar(Thread   t) { thread = t; }
35          synchronized Thread   get() { return thread; }
36          synchronized void clear() { thread = null; }
37      }
38  
39      private ThreadVar threadVar;
40  
41      /** 
42       * Get the value produced by the worker thread, or null if it 
43       * hasn't been constructed yet.
44       */
45      protected synchronized Object   getValue() { 
46          return value; 
47      }
48  
49      /** 
50       * Set the value produced by worker thread 
51       */
52      private synchronized void setValue(Object   x) { 
53          value = x; 
54      }
55  
56      /** 
57       * Compute the value to be returned by the <code>get</code> method. 
58       */
59      public abstract Object   construct();
60  
61      /**
62       * Called on the event dispatching thread (not on the worker thread)
63       * after the <code>construct</code> method has returned.
64       */
65      public void finished() {
66      }
67  
68      /**
69       * A new method that interrupts the worker thread.  Call this method
70       * to force the worker to stop what it's doing.
71       */
72      public void interrupt() {
73          Thread   t = threadVar.get();
74          if (t != null) {
75              t.interrupt();
76          }
77          threadVar.clear();
78      }
79  
80      /**
81       * Return the value created by the <code>construct</code> method.  
82       * Returns null if either the constructing thread or the current
83       * thread was interrupted before a value was produced.
84       * 
85       * @return the value created by the <code>construct</code> method
86       */
87      public Object   get() {
88          while (true) {  
89              Thread   t = threadVar.get();
90              if (t == null) {
91                  return getValue();
92              }
93              try {
94                  t.join();
95              }
96              catch (InterruptedException   e) {
97                  Thread.currentThread().interrupt(); // propagate
98                  return null;
99              }
100         }
101     }
102 
103 
104     /**
105      * Start a thread that will call the <code>construct</code> method
106      * and then exit.
107      */
108     public SwingWorker() {
109         final Runnable   doFinished = new Runnable  () {
110            public void run() { finished(); }
111         };
112 
113         Runnable   doConstruct = new Runnable  () { 
114             public void run() {
115                 try {
116                     setValue(construct());
117                 }
118                 finally {
119                     threadVar.clear();
120                 }
121 
122                 SwingUtilities.invokeLater(doFinished);
123             }
124         };
125 
126         Thread   t = new Thread  (doConstruct);
127         threadVar = new ThreadVar(t);
128     }
129 
130     /**
131      * Start the worker thread.
132      */
133     public void start() {
134         Thread   t = threadVar.get();
135         if (t != null) {
136             t.start();
137         }
138     }
139 }
140
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