Java tutorial
/* * 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.jackrabbit.oak.osgi; import static com.google.common.base.Preconditions.checkNotNull; import static com.google.common.base.Preconditions.checkState; import static com.google.common.collect.Maps.newHashMap; import java.io.Closeable; import java.util.Map; import javax.annotation.Nonnull; import com.google.common.io.Closeables; import org.apache.jackrabbit.oak.spi.commit.Observable; import org.apache.jackrabbit.oak.spi.commit.Observer; import org.osgi.framework.BundleContext; import org.osgi.framework.ServiceReference; import org.osgi.util.tracker.ServiceTracker; import org.osgi.util.tracker.ServiceTrackerCustomizer; public class ObserverTracker implements ServiceTrackerCustomizer { private final Map<ServiceReference, Closeable> subscriptions = newHashMap(); private final Observable observable; private BundleContext bundleContext; private ServiceTracker observerTracker; public ObserverTracker(@Nonnull Observable observable) { this.observable = checkNotNull(observable); } public void start(@Nonnull BundleContext bundleContext) { checkState(this.bundleContext == null); this.bundleContext = checkNotNull(bundleContext); observerTracker = new ServiceTracker(bundleContext, Observer.class.getName(), this); observerTracker.open(); } public void stop() { checkState(this.bundleContext != null); observerTracker.close(); } //------------------------< ServiceTrackerCustomizer >---------------------- @Override public Object addingService(ServiceReference reference) { Object service = bundleContext.getService(reference); if (service instanceof Observer) { subscriptions.put(reference, observable.addObserver((Observer) service)); return service; } else { bundleContext.ungetService(reference); return null; } } @Override public void modifiedService(ServiceReference reference, Object service) { // nothing to do } @Override public void removedService(ServiceReference reference, Object service) { Closeable subscription = subscriptions.remove(reference); if (subscription != null) { Closeables.closeQuietly(subscription); bundleContext.ungetService(reference); } } }