001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 *  or more contributor license agreements.  See the NOTICE file
004 *  distributed with this work for additional information
005 *  regarding copyright ownership.  The ASF licenses this file
006 *  to you under the Apache License, Version 2.0 (the
007 *  "License"); you may not use this file except in compliance
008 *  with the License.  You may obtain a copy of the License at
009 *
010 *       http://www.apache.org/licenses/LICENSE-2.0
011 *
012 *  Unless required by applicable law or agreed to in writing, software
013 *  distributed under the License is distributed on an "AS IS" BASIS,
014 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 *  See the License for the specific language governing permissions and
016 *  limitations under the License.
017 */
018
019package org.apache.hadoop.service;
020
021import org.apache.commons.logging.Log;
022import org.apache.commons.logging.LogFactory;
023import org.apache.hadoop.classification.InterfaceAudience.Public;
024import org.apache.hadoop.classification.InterfaceStability.Evolving;
025
026/**
027 * This is a state change listener that logs events at INFO level
028 */
029@Public
030@Evolving
031public class LoggingStateChangeListener implements ServiceStateChangeListener {
032
033  private static final Log LOG = LogFactory.getLog(LoggingStateChangeListener.class);
034
035  private final Log log;
036
037  /**
038   * Log events to the given log
039   * @param log destination for events
040   */
041  public LoggingStateChangeListener(Log log) {
042    //force an NPE if a null log came in
043    log.isDebugEnabled();
044    this.log = log;
045  }
046
047  /**
048   * Log events to the static log for this class
049   */
050  public LoggingStateChangeListener() {
051    this(LOG);
052  }
053
054  /**
055   * Callback for a state change event: log it
056   * @param service the service that has changed.
057   */
058  @Override
059  public void stateChanged(Service service) {
060    log.info("Entry to state "  + service.getServiceState()
061                 + " for " + service.getName());
062  }
063}