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/*
* Copyright (c) OSGi Alliance (2000, 2013). 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.service.log;
import java.util.Enumeration;
/**
* Provides methods to retrieve {@code LogEntry} objects from the log.
* <p>
* There are two ways to retrieve {@code LogEntry} objects:
* <ul>
* <li>The primary way to retrieve {@code LogEntry} objects is to register a
* {@code LogListener} object whose {@code LogListener.logged} method will be
* called for each entry added to the log.</li>
* <li>To retrieve past {@code LogEntry} objects, the {@code getLog} method can
* be called which will return an {@code Enumeration} of all {@code LogEntry}
* objects in the log.</li>
* </ul>
*
* @ThreadSafe
* @author $Id$
* @see LogEntry
* @see LogListener
* @see LogListener#logged(LogEntry)
*/
public interface LogReaderService {
/**
* Subscribes to {@code LogEntry} objects.
*
* <p>
* This method registers a {@code LogListener} object with the Log Reader
* Service. The {@code LogListener.logged(LogEntry)} method will be called
* for each {@code LogEntry} object placed into the log.
*
* <p>
* When a bundle which registers a {@code LogListener} object is stopped or
* otherwise releases the Log Reader Service, the Log Reader Service must
* remove all of the bundle's listeners.
*
* <p>
* If this Log Reader Service's list of listeners already contains a
* listener {@code l} such that {@code (l==listener)}, this method does
* nothing.
*
* @param listener A {@code LogListener} object to register; the
* {@code LogListener} object is used to receive {@code LogEntry}
* objects.
* @see LogListener
* @see LogEntry
* @see LogListener#logged(LogEntry)
*/
public void addLogListener(LogListener listener);
/**
* Unsubscribes to {@code LogEntry} objects.
*
* <p>
* This method unregisters a {@code LogListener} object from the Log Reader
* Service.
*
* <p>
* If {@code listener} is not contained in this Log Reader Service's list of
* listeners, this method does nothing.
*
* @param listener A {@code LogListener} object to unregister.
* @see LogListener
*/
public void removeLogListener(LogListener listener);
/**
* Returns an {@code Enumeration} of all {@code LogEntry} objects in the
* log.
*
* <p>
* Each element of the enumeration is a {@code LogEntry} object, ordered
* with the most recent entry first. Whether the enumeration is of all
* {@code LogEntry} objects since the Log Service was started or some recent
* past is implementation-specific. Also implementation-specific is whether
* informational and debug {@code LogEntry} objects are included in the
* enumeration.
*
* @return An {@code Enumeration} of all {@code LogEntry} objects in the
* log.
*/
public Enumeration getLog();
}
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