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The Pax Logging API Library is to allow for the Pax Logging Service to be reloaded without stopping the many dependent bundles. It also contains the OSGi Log Service API and the Knopflerfish Log API.

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/*
 * $Header: /cvshome/build/org.osgi.service.log/src/org/osgi/service/log/LogReaderService.java,v 1.10 2006/06/16 16:31:49 hargrave Exp $
 *
 * Copyright (c) OSGi Alliance (2000, 2006). 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 LogEntry objects from the log.
 * 
 * There are two ways to retrieve LogEntry objects:
 * 
 * The primary way to retrieve LogEntry objects is to register a
 * LogListener object whose LogListener.logged method will
 * be called for each entry added to the log.
 * To retrieve past LogEntry objects, the getLog
 * method can be called which will return an Enumeration of all
 * LogEntry objects in the log.
 * 
 * @version $Revision: 1.10 $
 * @see LogEntry
 * @see LogListener
 * @see LogListener#logged(LogEntry)
 */
public interface LogReaderService {
	/**
	 * Subscribes to LogEntry objects.
	 * 
	 * 
	 * This method registers a LogListener object with the Log Reader
	 * Service. The LogListener.logged(LogEntry) method will be
	 * called for each LogEntry object placed into the log.
	 * 
	 * 

	 * When a bundle which registers a LogListener object is stopped
	 * or otherwise releases the Log Reader Service, the Log Reader Service must
	 * remove all of the bundle's listeners.
	 * 
	 * 

	 * If this Log Reader Service's list of listeners already contains a
	 * listener l such that (l==listener), this method
	 * does nothing.
	 * 
	 * @param listener A LogListener object to register; the
	 *        LogListener object is used to receive LogEntry
	 *        objects.
	 * @see LogListener
	 * @see LogEntry
	 * @see LogListener#logged(LogEntry)
	 */
	public void addLogListener(LogListener listener);

	/**
	 * Unsubscribes to LogEntry objects.
	 * 
	 * 

	 * This method unregisters a LogListener object from the Log
	 * Reader Service.
	 * 
	 * 

	 * If listener is not contained in this Log Reader Service's list
	 * of listeners, this method does nothing.
	 * 
	 * @param listener A LogListener object to unregister.
	 * @see LogListener
	 */
	public void removeLogListener(LogListener listener);

	/**
	 * Returns an Enumeration of all LogEntry objects in
	 * the log.
	 * 
	 * 
	 * Each element of the enumeration is a LogEntry object, ordered
	 * with the most recent entry first. Whether the enumeration is of all
	 * LogEntry objects since the Log Service was started or some
	 * recent past is implementation-specific. Also implementation-specific is
	 * whether informational and debug LogEntry objects are included
	 * in the enumeration.
	 * @return An Enumeration of all LogEntry objects in
	 * the log.
	 */
	public Enumeration getLog();
}