SwingWorker


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