1 files changed, 147 insertions, 0 deletions
diff --git a/watchmaker/swing/src/java/main/org/uncommons/swing/SwingBackgroundTask.java b/watchmaker/swing/src/java/main/org/uncommons/swing/SwingBackgroundTask.java
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+++ b/watchmaker/swing/src/java/main/org/uncommons/swing/SwingBackgroundTask.java
@@ -0,0 +1,147 @@
+//=============================================================================
+// Copyright 2006-2010 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 <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 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);
+    }
+}