org.uncommons.swing.SwingBackgroundTask Maven / Gradle / Ivy
// ============================================================================
// Copyright 2006-2009 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 java.util.concurrent.atomic.AtomicInteger;
import javax.swing.JOptionPane;
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 Type of result generated by the task.
*/
public abstract class SwingBackgroundTask
{
// Used to assign thread IDs to make threads easier to identify when debugging.
private static final AtomicInteger INSTANCE_COUNT = new AtomicInteger(0);
private final CountDownLatch latch = new CountDownLatch(1);
private final int id;
protected SwingBackgroundTask()
{
this.id = INSTANCE_COUNT.getAndIncrement();
}
/**
* Asynchronous call that begins execution of the task and returns immediately.
* The {@link #performTask()} method will be invoked on a background thread and,
* when it has completed, {@link #postProcessing(Object)} will be invoked on the
* Event Dispatch Thread (or, if there is an exception, {@link #onError(Throwable)}
* will be invoked instead - also on the EDT).
* @see #performTask()
* @see #postProcessing(Object)
* @see #onError(Throwable)
* @see #waitForCompletion()
*/
public void execute()
{
Runnable task = new Runnable()
{
public void run()
{
try
{
final V result = performTask();
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
postProcessing(result);
latch.countDown();
}
});
}
// If an exception occurs performing the task, we need
// to handle it.
catch (final Throwable throwable)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
onError(throwable);
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.
* @throws Exception The task may throw an exception, in which case
* the {@link #onError(Throwable)} method will be invoked instead of
* {@link #postProcessing(Object)}.
*/
protected abstract V performTask() throws Exception;
/**
* This method is invoked, on the Event Dispatch Thread, after the task
* has been executed.
* This empty default implementation should be over-ridden in sub-classes
* in order to provide GUI updates that should occur following successful
* task completion.
* @param result The result from the {@link #performTask()} method.
*/
protected void postProcessing(V result)
{
// Over-ride in sub-class.
}
/**
* This method is invoked, on the Event Dispatch Thread, if there is an
* exception or error executing the {@link #performTask()} method.
* This default implementation displays a message dialog with details of the
* exception. It may be over-ridden in sub-classes.
* @param throwable The exception or error that was thrown while executing
* the task.
*/
protected void onError(Throwable throwable)
{
throwable.printStackTrace();
JOptionPane.showMessageDialog(null,
throwable.getMessage(),
throwable.getClass().getName(),
JOptionPane.ERROR_MESSAGE);
}
}