ipojo/src/main/java/org/osgi/service/log/LogReaderService.java

/*
 * $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 <code>LogEntry</code> objects from the log.
 * <p>
 * There are two ways to retrieve <code>LogEntry</code> objects:
 * <ul>
 * <li>The primary way to retrieve <code>LogEntry</code> objects is to
 * register a <code>LogListener</code> object whose
 * <code>LogListener.logged</code> method will be called for each entry added
 * to the log.
 * <li>To retrieve past <code>LogEntry</code> objects, the
 * <code>getLog</code> method can be called which will return an
 * <code>Enumeration</code> of all <code>LogEntry</code> objects in the log.
 * 
 * @version $Revision: 1.10 $
 * @see LogEntry
 * @see LogListener
 * @see LogListener#logged(LogEntry)
 */
public interface LogReaderService {
    /**
     * Subscribes to <code>LogEntry</code> objects.
     * 
     * <p>
     * This method registers a <code>LogListener</code> object with the Log
     * Reader Service. The <code>LogListener.logged(LogEntry)</code> method
     * will be called for each <code>LogEntry</code> object placed into the
     * log.
     * 
     * <p>
     * When a bundle which registers a <code>LogListener</code> 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</code> such that <code>(l==listener)</code>, this
     * method does nothing.
     * 
     * @param listener A <code>LogListener</code> object to register; the
     * <code>LogListener</code> object is used to receive
     * <code>LogEntry</code> objects.
     * @see LogListener
     * @see LogEntry
     * @see LogListener#logged(LogEntry)
     */
    public void addLogListener(LogListener listener);

    /**
     * Unsubscribes to <code>LogEntry</code> objects.
     * 
     * <p>
     * This method unregisters a <code>LogListener</code> object from the Log
     * Reader Service.
     * 
     * <p>
     * If <code>listener</code> is not contained in this Log Reader Service's
     * list of listeners, this method does nothing.
     * 
     * @param listener A <code>LogListener</code> object to unregister.
     * @see LogListener
     */
    public void removeLogListener(LogListener listener);

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