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// ============================================================================
// Copyright 2006-2012 Daniel W. Dyer
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ============================================================================
package org.uncommons.swing;
import java.util.concurrent.CountDownLatch;
import javax.swing.SwingUtilities;
/**
* A task that is executed on a background thread and then updates
* a Swing GUI. A task may only be executed once.
* @author Daniel Dyer
* @param <V> Type of result generated by the task.
*/
public abstract class SwingBackgroundTask<V>
{
// Used to assign thread IDs to make threads easier to identify when debugging.
private static int instanceCount = 0;
private final CountDownLatch latch = new CountDownLatch(1);
private final int id;
protected SwingBackgroundTask()
{
synchronized (SwingBackgroundTask.class)
{
this.id = instanceCount;
++instanceCount;
}
}
/**
* Asynchronous call that begins execution of the task
* and returns immediately.
*/
public void execute()
{
Runnable task = new Runnable()
{
public void run()
{
final V result = performTask();
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
postProcessing(result);
latch.countDown();
}
});
}
};
new Thread(task, "SwingBackgroundTask-" + id).start();
}
/**
* Waits for the execution of this task to complete. If the {@link #execute()}
* method has not yet been invoked, this method will block indefinitely.
* @throws InterruptedException If the thread executing the task
* is interrupted.
*/
public void waitForCompletion() throws InterruptedException
{
latch.await();
}
/**
* Performs the processing of the task and returns a result.
* Implement in sub-classes to provide the task logic. This method will
* run on a background thread and not on the Event Dispatch Thread and
* therefore should not manipulate any Swing components.
* @return The result of executing this task.
*/
protected abstract V performTask();
/**
* This method is invoked, on the Event Dispatch Thread, after the task
* has been executed.
* This should be implemented in sub-classes in order to provide GUI
* updates that should occur following task completion.
* @param result The result from the {@link #performTask()} method.
*/
protected abstract void postProcessing(V result);
}
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