ShapeTracker.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.foo.paint;

import java.util.Dictionary;
import javax.swing.*;
import org.foo.shape.SimpleShape;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;

/**
 * Extends the <tt>BundleTracker</tt> to create a tracker for
 * <tt>SimpleShape</tt> extensions. The tracker is responsible for listening for
 * <tt>SimpleShape</tt> extensions and informing the application about the
 * availability of shapes. This tracker forces all notifications to be processed
 * on the Swing event thread to avoid synchronization and redraw issues.
 **/
public class ShapeTracker extends BundleTracker {
  // Flag indicating an added shape.
  private static final int ADDED = 1;
  // Flag indicating a removed shape.
  private static final int REMOVED = 2;
  // The bundle context used for tracking.
  private BundleContext m_context;
  // The application object to notify.
  private PaintFrame m_frame;

  /**
   * Constructs a tracker that uses the specified bundle context to track
   * extensions and notifies the specified application object about changes.
   * 
   * @param context The bundle context to be used by the tracker.
   * @param frame The application object to notify about extension changes.
   **/
  public ShapeTracker(BundleContext context, PaintFrame frame) {
    super(context);
    m_context = context;
    m_frame = frame;
  }

  /**
   * Overrides the <tt>BundleTracker</tt> functionality to inform the
   * application object about the added extensions.
   * 
   * @param bundle The activated bundle.
   **/
  protected void addedBundle(Bundle bundle) {
    processBundleOnEventThread(ADDED, bundle);
  }

  /**
   * Overrides the <tt>BundleTracker</tt> functionality to inform the
   * application object about removed extensions.
   * 
   * @param bundle The inactivated bundle.
   **/
  protected void removedBundle(Bundle bundle) {
    processBundleOnEventThread(REMOVED, bundle);
  }

  /**
   * Processes a received bundle notification from the <tt>BundleTracker</tt>,
   * forcing the processing of the notification onto the Swing event thread if
   * it is not already on it.
   * 
   * @param action The type of action associated with the notification.
   * @param bundle The bundle of the corresponding extension.
   **/
  private void processBundleOnEventThread(int action, Bundle bundle) {
    if ((m_context.getBundle(0).getState() & (Bundle.STARTING | Bundle.ACTIVE)) == 0) {
      return;
    }

    try {
      if (SwingUtilities.isEventDispatchThread()) {
        processBundle(action, bundle);
      } else {
        SwingUtilities.invokeAndWait(new BundleRunnable(action, bundle));
      }
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }

  /**
   * Actually performs the processing of the bundle notification. Invokes the
   * appropriate callback method on the application object depending on the
   * action type of the notification.
   * 
   * @param action The type of action associated with the notification.
   * @param bundle The bundle of the corresponding extension.
   **/
  private void processBundle(int action, Bundle bundle) {
    Dictionary dict = bundle.getHeaders();

    // Try to get the name of the extension.
    String name = (String) dict.get(SimpleShape.NAME_PROPERTY);
    // Return immediately if the bundle is not an extension.
    if (name == null) {
      return;
    }

    switch (action) {
      case ADDED:
        // Get the icon resource of the extension.
        String iconPath = (String) dict.get(SimpleShape.ICON_PROPERTY);
        Icon icon = new ImageIcon(bundle.getResource(iconPath));
        // Get the class of the extension.
        String className = (String) dict.get(SimpleShape.CLASS_PROPERTY);
        m_frame.addShape(name, icon, new DefaultShape(m_context, bundle.getBundleId(), className));
        break;

      case REMOVED:
        m_frame.removeShape(name);
        break;
    }
  }

  /**
   * Simple class used to process bundle notification handling on the Swing
   * event thread.
   **/
  private class BundleRunnable implements Runnable {
    private int m_action;
    private Bundle m_bundle;

    /**
     * Constructs an object with the specified action and bundle object for
     * processing on the Swing event thread.
     * 
     * @param action The type of action associated with the notification.
     * @param bundle The bundle of the corresponding extension.
     **/
    public BundleRunnable(int action, Bundle bundle) {
      m_action = action;
      m_bundle = bundle;
    }

    /**
     * Calls the <tt>processBundle()</tt> method.
     **/
    public void run() {
      processBundle(m_action, m_bundle);
    }
  }
}