EDU.oswego.cs.dl.util.concurrent.misc

Class SwingWorker

public abstract class SwingWorker extends ThreadFactoryUser implements Runnable

An abstract class that you subclass to perform GUI-related work in a dedicated thread.

This class was adapted from the SwingWorker written by Hans Muller and presented in "Using a Swing Worker Thread" in the Swing Connection - http://java.sun.com/products/jfc/tsc/articles/threads/threads2.html

A closely related version of this class is described in "The Last Word in Swing Threads" in the Swing Connection - http://java.sun.com/products/jfc/tsc/articles/threads/threads3.html

This SwingWorker is a ThreadFactoryUser and implements Runnable. The default thread factory creates low-priority worker threads. A special constructor is provided for enabling a timeout. When the timeout expires, the worker thread is interrupted.

Note: Using a timeout of Long.MAX_VALUE will not impose a timeout but will create an additional thread of control that will respond to an interrupt even if the construct implementation ignores them.

Sample Usage

 import EDU.oswego.cs.dl.util.concurrent.TimeoutException;
 import EDU.oswego.cs.dl.util.concurrent.misc.SwingWorker;

 public class SwingWorkerDemo extends javax.swing.JApplet {

   private static final int TIMEOUT = 5000; // 5 seconds
   private javax.swing.JLabel status;
   private javax.swing.JButton start;
   private SwingWorker worker;

   public SwingWorkerDemo() {
     status = new javax.swing.JLabel("Ready");
     status.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);
     getContentPane().add(status, java.awt.BorderLayout.CENTER);
     start = new javax.swing.JButton("Start");
     getContentPane().add(start, java.awt.BorderLayout.SOUTH);

     start.addActionListener(new java.awt.event.ActionListener() {
       public void actionPerformed(java.awt.event.ActionEvent evt) {
         if (start.getText().equals("Start")) {
           start.setText("Stop");
           status.setText("Working...");
           worker = new DemoSwingWorker(TIMEOUT);
           worker.start();
         } else {
           worker.interrupt();
         }
       }
     });
   }

   private class DemoSwingWorker extends SwingWorker {
     private static final java.util.Random RAND = new java.util.Random();
     public DemoSwingWorker(long msecs) {
       super(msecs);
     }
     protected Object construct() throws InterruptedException {
       // Take a random nap. If we oversleep, the worker times out.
       Thread.sleep(RAND.nextInt(2*TIMEOUT));
       return "Success";
     }
     protected void finished() {
       start.setText("Start");
       try {
         Object result = get();
         status.setText((String) result);
       }
       catch (java.lang.reflect.InvocationTargetException e) {
         Throwable ex = e.getTargetException();
         if (ex instanceof TimeoutException) {
           status.setText("Timed out.");
         } else if (ex instanceof InterruptedException) {
           status.setText("Interrupted.");
         } else {
           status.setText("Exception: " + ex);
         }
       }
       catch (InterruptedException ex) {
         // event-dispatch thread won't be interrupted 
         throw new IllegalStateException(ex+"");
       }
     }
   }
 }
 

Version: 3.0

[ Introduction to this package. ]

Author: Joseph Bowbeer Hans Muller

Constructor Summary
SwingWorker()
Creates new SwingWorker with no timeout.
SwingWorker(long msecs)
Creates new SwingWorker with specified timeout.
protected SwingWorker(ThreadFactory factory, long msecs)
Creates new SwingWorker with specified thread factory and timeout.
Method Summary
protected abstract Objectconstruct()
Computes the value to be returned by the get method.
protected voidfinished()
Called on the event dispatching thread (not on the worker thread) after the construct method has returned.
Objectget()
Return the value created by the construct method, waiting if necessary until it is ready.
InvocationTargetExceptiongetException()
Get the exception, or null if there isn't one (yet).
longgetTimeout()
Returns timeout period in milliseconds.
voidinterrupt()
Stops the worker and sets the exception to InterruptedException.
booleanisReady()
Return whether the get method is ready to return a value.
voidrun()
Calls the construct method to compute the result, and then invokes the finished method on the event dispatch thread.
voidstart()
Starts the worker thread.
ObjecttimedGet(long msecs)
Wait at most msecs to access the constructed result.

Constructor Detail

SwingWorker

public SwingWorker()
Creates new SwingWorker with no timeout.

SwingWorker

public SwingWorker(long msecs)
Creates new SwingWorker with specified timeout.

Parameters: msecs timeout in milliseconds, or 0 for no time limit.

SwingWorker

protected SwingWorker(ThreadFactory factory, long msecs)
Creates new SwingWorker with specified thread factory and timeout.

Parameters: factory factory for worker threads. msecs timeout in milliseconds, or 0 for no time limit.

Method Detail

construct

protected abstract Object construct()
Computes the value to be returned by the get method.

finished

protected void finished()
Called on the event dispatching thread (not on the worker thread) after the construct method has returned.

get

public Object get()
Return the value created by the construct method, waiting if necessary until it is ready.

Returns: the value created by the construct method

Throws: InterruptedException if current thread was interrupted InvocationTargetException if the constructing thread encountered an exception or was interrupted.

getException

public InvocationTargetException getException()
Get the exception, or null if there isn't one (yet). This does not wait until the worker is ready, so should ordinarily only be called if you know it is.

Returns: the exception encountered by the construct method wrapped in an InvocationTargetException

getTimeout

public long getTimeout()
Returns timeout period in milliseconds. Timeout is the maximum time to wait for worker to complete. There is no time limit if timeout is 0 (default).

interrupt

public void interrupt()
Stops the worker and sets the exception to InterruptedException.

isReady

public boolean isReady()
Return whether the get method is ready to return a value.

Returns: true if a value or exception has been set. else false

run

public void run()
Calls the construct method to compute the result, and then invokes the finished method on the event dispatch thread.

start

public void start()
Starts the worker thread.

timedGet

public Object timedGet(long msecs)
Wait at most msecs to access the constructed result.

Returns: current value

Throws: TimeoutException if not ready after msecs InterruptedException if current thread has been interrupted InvocationTargetException if the constructing thread encountered an exception or was interrupted.