/*
 * Copyright (c) OSGi Alliance (2000, 2017). 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;

import org.osgi.annotation.versioning.ProviderType;

LogReaderService for obtaining logging information.
 Since 1.4, LogStreamProvider is the preferred way to obtain LogEntry objects. 
 The LogReaderService provides two ways to obtain LogEntry objects: 

The primary way to retrieve LogEntry objects is to register a LogListener object whose LogListener.logged(LogEntry) method will be called for each entry added to the log.
To obtain past LogEntry objects, the getLog() method can be called which will return an Enumeration of the LogEntry objects in the log.

Author:
$Id: 2e91c2e5529e81021b46af1dbaabee13251c7a61 $
@ThreadSafe
/**
 * LogReaderService for obtaining logging information.
 * <p>
 * Since 1.4, {@link org.osgi.service.log.stream.LogStreamProvider} is the
 * preferred way to obtain {@link LogEntry} objects.
 * <p>
 * The LogReaderService provides two ways to obtain {@link LogEntry} objects:
 * <ul>
 * <li>The primary way to retrieve {@link LogEntry} objects is to register a
 * {@link LogListener} object whose {@link LogListener#logged(LogEntry)} method
 * will be called for each entry added to the log.</li>
 * <li>To obtain past {@link LogEntry} objects, the {@link #getLog()} method can
 * be called which will return an {@code Enumeration} of the {@link LogEntry}
 * objects in the log.</li>
 * </ul>
 * 
 * @ThreadSafe
 * @author $Id: 2e91c2e5529e81021b46af1dbaabee13251c7a61 $
 */
@ProviderType
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. 
 Since 1.4, LogStreamProvider is the preferred way to obtain LogEntry objects. 
Params:
listener – A LogListener object to register; the LogListener object is used to receive LogEntry objects./**
	 * Subscribes to {@link LogEntry} objects.
	 * <p>
	 * This method registers a {@link LogListener} object with the Log Reader
	 * Service. The {@link LogListener#logged(LogEntry)} method will be called
	 * for each {@link LogEntry} object placed into the log.
	 * <p>
	 * When a bundle which registers a {@link 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.
	 * <p>
	 * Since 1.4, {@link org.osgi.service.log.stream.LogStreamProvider} is the
	 * preferred way to obtain {@link LogEntry} objects.
	 * 
	 * @param listener A {@link LogListener} object to register; the
	 *            {@link LogListener} object is used to receive {@link LogEntry}
	 *            objects.
	 */
	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. 
 Since 1.4, LogStreamProvider is the preferred way to obtain LogEntry objects. 
Params:
listener – A LogListener object to unregister./**
	 * Unsubscribes to {@link LogEntry} objects.
	 * <p>
	 * This method unregisters a {@link 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.
	 * <p>
	 * Since 1.4, {@link org.osgi.service.log.stream.LogStreamProvider} is the
	 * preferred way to obtain {@link LogEntry} objects.
	 * 
	 * @param listener A {@link LogListener} object to unregister.
	 */
	void removeLogListener(LogListener listener);

	
Returns an Enumeration of the 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. 
Returns:
An Enumeration of the LogEntry objects in the log./**
	 * Returns an {@code Enumeration} of the {@link LogEntry} objects in the
	 * log.
	 * <p>
	 * Each element of the enumeration is a {@link LogEntry} object, ordered
	 * with the most recent entry first. Whether the enumeration is of all
	 * {@link LogEntry} objects since the Log Service was started or some recent
	 * past is implementation-specific.
	 * 
	 * @return An {@code Enumeration} of the {@link LogEntry} objects in the
	 *         log.
	 */
	Enumeration<LogEntry> getLog();
}