SwingWorker.java

package ilarkesto.swing;

import javax.swing.SwingUtilities;

/**
 * This is the 3rd version of SwingWorker (also known as SwingWorker 3), an abstract class that you subclass
 * to perform GUI-related work in a dedicated thread. For instructions on and examples of using this class,
 * see: http://java.sun.com/docs/books/tutorial/uiswing/misc/threads.html Note that the API changed slightly
 * in the 3rd version: You must now invoke start() on the SwingWorker after creating it.
 */
public abstract class SwingWorker {

	private Object	value;	// see getValue(), setValue()

	/**
	 * Class to maintain reference to current worker thread under separate synchronization control.
	 */
	private static class ThreadVar {

		private Thread	thread;

		ThreadVar(Thread t) {
			thread = t;
		}

		synchronized Thread get() {
			return thread;
		}

		synchronized void clear() {
			thread = null;
		}
	}

	private ThreadVar	threadVar;

	/**
	 * Get the value produced by the worker thread, or null if it hasn't been constructed yet.
	 */
	protected synchronized Object getValue() {
		return value;
	}

	/**
	 * Set the value produced by worker thread
	 */
	private synchronized void setValue(Object x) {
		value = x;
	}

	/**
	 * Compute the value to be returned by the <code>get</code> method.
	 */
	public abstract Object construct();

	/**
	 * Called on the event dispatching thread (not on the worker thread) after the <code>construct</code>
	 * method has returned.
	 */
	public void finished() {}

	/**
	 * A new method that interrupts the worker thread. Call this method to force the worker to stop what it's
	 * doing.
	 */
	public void interrupt() {
		Thread t = threadVar.get();
		if (t != null) {
			t.interrupt();
		}
		threadVar.clear();
	}

	/**
	 * Return the value created by the <code>construct</code> method. Returns null if either the
	 * constructing thread or the current thread was interrupted before a value was produced.
	 * 
	 * @return the value created by the <code>construct</code> method
	 */
	public Object get() {
		while (true) {
			Thread t = threadVar.get();
			if (t == null) { return getValue(); }
			try {
				t.join();
			} catch (InterruptedException e) {
				Thread.currentThread().interrupt(); // propagate
				return null;
			}
		}
	}

	/**
	 * Start a thread that will call the <code>construct</code> method and then exit.
	 */
	public SwingWorker() {
		final Runnable doFinished = new Runnable() {

			public void run() {
				finished();
			}
		};

		Runnable doConstruct = new Runnable() {

			public void run() {
				try {
					setValue(construct());
				} finally {
					threadVar.clear();
				}

				SwingUtilities.invokeLater(doFinished);
			}
		};

		Thread t = new Thread(doConstruct);
		threadVar = new ThreadVar(t);
	}

	/**
	 * Start the worker thread.
	 */
	public void start() {
		Thread t = threadVar.get();
		if (t != null) {
			t.start();
		}
	}

	public static void start(final Runnable service, final Runnable swing) {
		new SwingWorker() {

			public Object construct() {
				service.run();
				// try {
				// Thread.sleep(500);
				// } catch (InterruptedException ex) {
				// throw new RuntimeException(ex);
				// }
				return service;
			}

			public void finished() {
				if (swing != null) swing.run();
			}

		}.start();
	}

}