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
019 package org.apache.hadoop.service;
020
021 import org.apache.commons.logging.Log;
022 import org.apache.commons.logging.LogFactory;
023 import org.apache.hadoop.classification.InterfaceAudience.Public;
024 import 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
031 public 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 }