BundleTracker.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.apache.felix.ipojo.handler.extender;

import java.util.HashSet;
import java.util.Set;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.BundleEvent;
import org.osgi.framework.SynchronousBundleListener;

/**
 * This is a very simple bundle tracker utility class that tracks active
 * bundles. The tracker must be given a bundle context upon creation,
 * which it uses to listen for bundle events. The bundle tracker must be
 * opened to track objects and closed when it is no longer needed. This
 * class is abstract, which means in order to use it you must create a
 * subclass of it. Subclasses must implement the <tt>addedBundle()</tt>
 * and <tt>removedBundle()</tt> methods, which can be used to perform some
 * custom action upon the activation or deactivation of bundles. Since this
 * tracker is quite simple, its concurrency control approach is also
 * simplistic. This means that subclasses should take great care to ensure
 * that their <tt>addedBundle()</tt> and <tt>removedBundle()</tt> methods
 * are very simple and do not do anything to change the state of any bundles.
 * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
 **/
public abstract class BundleTracker {
    /**
     * Set of tracked bundles.
     */
    final Set m_bundleSet = new HashSet();

    /**
     * Bundle context.
     */
    final BundleContext m_context;

    /**
     * Synchronous bundle listener.
     */
    final SynchronousBundleListener m_listener;

    /**
     * Flag indicating if the tracking is open.
     */
    boolean m_open;

    /**
     * Constructs a bundle tracker object that will use the specified
     * bundle context.
     * @param context the bundle context to use to track bundles.
     **/
    public BundleTracker(BundleContext context) {
        m_context = context;
        m_listener = new SynchronousBundleListener() {
            public void bundleChanged(BundleEvent evt) {
                synchronized (BundleTracker.this) {
                    if (!m_open) { return; }

                    if (evt.getType() == BundleEvent.STARTED) {
                        if (!m_bundleSet.contains(evt.getBundle())) {
                            m_bundleSet.add(evt.getBundle());
                            addedBundle(evt.getBundle());
                        }
                    } else if (evt.getType() == BundleEvent.STOPPED) {
                        if (m_bundleSet.contains(evt.getBundle())) {
                            m_bundleSet.remove(evt.getBundle());
                            removedBundle(evt.getBundle());
                        }
                    }
                }
            }
        };
    }

    /**
     * Returns the current set of active bundles.
     * @return the current set of active bundles.
     **/
    public synchronized Bundle[] getBundles() {
        return (Bundle[]) m_bundleSet.toArray(new Bundle[m_bundleSet.size()]);
    }

    /**
     * Call this method to start the tracking of active bundles.
     **/
    public void open() {
        synchronized (this) {
            if (!m_open) {
                m_open = true;

                m_context.addBundleListener(m_listener);
            }
        }

        Bundle[] bundles = m_context.getBundles();
        for (int i = 0; i < bundles.length; i++) {
            if (bundles[i].getState() == Bundle.ACTIVE) {
                if (m_bundleSet.add(bundles[i])) {
                    addedBundle(bundles[i]);
                }
            }
        }
    }

    /**
     * Call this method to stop the tracking of active bundles.
     **/
    public synchronized void close() {
        if (m_open) {
            m_open = false;

            m_context.removeBundleListener(m_listener);

            Bundle[] bundles = (Bundle[]) m_bundleSet.toArray(new Bundle[m_bundleSet.size()]);
            for (int i = 0; i < bundles.length; i++) {
                if (m_bundleSet.remove(bundles[i])) {
                    removedBundle(bundles[i]);
                }
            }
        }
    }

    /**
     * Subclasses must implement this method; it can be used to perform
     * actions upon the activation of a bundle. Subclasses should keep
     * this method implementation as simple as possible and should not
     * cause the change in any bundle state to avoid concurrency issues.
     * @param bundle the bundle being added to the active set.
     **/
    protected abstract void addedBundle(Bundle bundle);

    /**
     * Subclasses must implement this method; it can be used to perform
     * actions upon the deactivation of a bundle. Subclasses should keep
     * this method implementation as simple as possible and should not
     * cause the change in any bundle state to avoid concurrency issues.
     * @param bundle the bundle being removed from the active set.
     **/
    protected abstract void removedBundle(Bundle bundle);
}