RecursiveBundleTracker.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.aries.util.tracker;

import org.apache.aries.util.tracker.hook.BundleHookBundleTracker;
import org.osgi.framework.Bundle;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.util.tracker.BundleTracker;
import org.osgi.util.tracker.BundleTrackerCustomizer;

/**
 * <p>This class supports the tracking of composite bundles. It allows clients to ignore any
 * events related to framework bundles, as it will automatically handle these events. In
 * order to use this class clients must create a subclass and implement the methods of the
 * <code>BundleTrackerCustomizer</code> interface. In spite of this, instances of this class
 * MUST NOT be passed as a parameter to any <code>BundleTracker</code>.</p>
 * <p/>
 * The model for using this is that classes should instantiate it
 * and pass it a 'vanilla' bundle tracker.
 *
 * @author pradine
 */
public final class RecursiveBundleTracker {
    private static final int COMPOSITE_BUNDLE_MASK =
            Bundle.INSTALLED | Bundle.RESOLVED | Bundle.STARTING | Bundle.ACTIVE | Bundle.STOPPING;

    private final BundleTracker tracker;
    private final BundleTracker compositeTracker;

    /**
     * Constructor
     *
     * @param context   - The <code>BundleContext</code> against which the tracking is done.
     * @param stateMask - The bit mask of the ORing of the bundle states to be tracked. The
     *                  mask must contain the flags <code>Bundle.INSTALLED | Bundle.RESOLVED | Bundle.STARTING | Bundle.ACTIVE | Bundle.STOPPING</code>
     *                  as a minimum.
     * @throws IllegalArgumentException - If the provided bit mask does not contain required
     *                                  flags
     */
    public RecursiveBundleTracker(BundleContext context, int stateMask, BundleTrackerCustomizer customizer) {
        //This test only makes sense for composite bundles, but in the interests of more consistent behavior lets leave it.
        // We always need INSTALLED events so we can recursively listen to the frameworks
        if ((stateMask & COMPOSITE_BUNDLE_MASK) != COMPOSITE_BUNDLE_MASK)
            throw new IllegalArgumentException();
        BundleTracker tracker = null;
        try {
            //R43, equinox composite bundles seem to produce appropriate bundle event hook notifications
            tracker = new BundleHookBundleTracker(context, stateMask, customizer);
        } catch (Throwable e) {
        }
        if (areMultipleFrameworksAvailable(context)) {
            compositeTracker = new InternalRecursiveBundleTracker(context, stateMask, customizer, tracker == null);
        } else {
            compositeTracker = null;
        }
        if (tracker == null && compositeTracker == null) {
            //R42
            tracker = new BundleTracker(context, stateMask, customizer);
        }
        this.tracker = tracker;
    }

    /*
     * Checks whether or not the framework supports composite bundles. The only
     * known supporting framework is Equinox. When the Equinox specific
     * framework property osgi.resolverMode is set to "strict", the
     * CompositeBundleFactory service is registered, but the x-internal
     * org.osgi.service.framework package is not exported, thus the need for
     * the additional Class.forName check.
     */
    private static boolean areMultipleFrameworksAvailable(BundleContext context) {
    	String compositeBundleFactory = "org.osgi.service.framework.CompositeBundleFactory";
    	try {
    		Class.forName(compositeBundleFactory);
    	} catch (ClassNotFoundException e) {
    		return false;
    	}
        ServiceReference sr = context.getServiceReference(compositeBundleFactory);
        return sr != null;
    }

    /**
     * Start tracking bundles that match the bit mask provided at creation time.
     *
     * @see BundleTracker#open()
     */
    public void open() {
        if (tracker != null) {
            tracker.open();
        }
        if (compositeTracker != null) {
            compositeTracker.open();
        }
    }

    /**
     * Stop the tracking of bundles
     *
     * @see BundleTracker#close()
     */
    public void close() {
        if (tracker != null) {
            tracker.close();
        }
        if (compositeTracker != null) {
            compositeTracker.close();
        }
    }

}