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/*
* Copyright (c) OSGi Alliance (2000, 2012). All Rights Reserved.
*
* 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.osgi.util.tracker;
import org.osgi.framework.ServiceReference;
/**
* The {@code ServiceTrackerCustomizer} interface allows a
* {@code ServiceTracker} to customize the service objects that are tracked. A
* {@code ServiceTrackerCustomizer} is called when a service is being added to a
* {@code ServiceTracker}. The {@code ServiceTrackerCustomizer} can then return
* an object for the tracked service. A {@code ServiceTrackerCustomizer} is also
* called when a tracked service is modified or has been removed from a
* {@code ServiceTracker}.
*
* <p>
* The methods in this interface may be called as the result of a
* {@code ServiceEvent} being received by a {@code ServiceTracker}. Since
* {@code ServiceEvent}s are synchronously delivered by the Framework, it is
* highly recommended that implementations of these methods do not register (
* {@code BundleContext.registerService}), modify (
* {@code ServiceRegistration.setProperties}) or unregister (
* {@code ServiceRegistration.unregister}) a service while being synchronized on
* any object.
*
* <p>
* The {@code ServiceTracker} class is thread-safe. It does not call a
* {@code ServiceTrackerCustomizer} while holding any locks.
* {@code ServiceTrackerCustomizer} implementations must also be thread-safe.
*
* @param <S> The type of the service being tracked.
* @param <T> The type of the tracked object.
* @ThreadSafe
* @version $Id: c14b8d47026b6bd4ba1f2db7bf7e755d00fc6f6a $
*/
public interface ServiceTrackerCustomizer<S, T> {
/**
* A service is being added to the {@code ServiceTracker}.
*
* <p>
* This method is called before a service which matched the search
* parameters of the {@code ServiceTracker} is added to the
* {@code ServiceTracker}. This method should return the service object to
* be tracked for the specified {@code ServiceReference}. The returned
* service object is stored in the {@code ServiceTracker} and is available
* from the {@code getService} and {@code getServices} methods.
*
* @param reference The reference to the service being added to the
* {@code ServiceTracker}.
* @return The service object to be tracked for the specified referenced
* service or {@code null} if the specified referenced service
* should not be tracked.
*/
public T addingService(ServiceReference<S> reference);
/**
* A service tracked by the {@code ServiceTracker} has been modified.
*
* <p>
* This method is called when a service being tracked by the
* {@code ServiceTracker} has had it properties modified.
*
* @param reference The reference to the service that has been modified.
* @param service The service object for the specified referenced service.
*/
public void modifiedService(ServiceReference<S> reference, T service);
/**
* A service tracked by the {@code ServiceTracker} has been removed.
*
* <p>
* This method is called after a service is no longer being tracked by the
* {@code ServiceTracker}.
*
* @param reference The reference to the service that has been removed.
* @param service The service object for the specified referenced service.
*/
public void removedService(ServiceReference<S> reference, T service);
}
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