SwingWorker


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