001 /**
002 *
003 * Copyright 2004 Protique Ltd
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 **/
018
019 package org.activemq.advisories;
020 import java.util.Iterator;
021 import java.util.List;
022 import java.util.Map;
023 import java.util.Set;
024 import javax.jms.Connection;
025 import javax.jms.Destination;
026 import javax.jms.JMSException;
027 import javax.jms.Message;
028 import javax.jms.MessageConsumer;
029 import javax.jms.MessageListener;
030 import javax.jms.ObjectMessage;
031 import javax.jms.Session;
032 import org.apache.commons.logging.Log;
033 import org.apache.commons.logging.LogFactory;
034 import org.activemq.message.ActiveMQDestination;
035 import org.activemq.message.ConsumerInfo;
036 import EDU.oswego.cs.dl.util.concurrent.ConcurrentHashMap;
037 import EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArrayList;
038 import EDU.oswego.cs.dl.util.concurrent.CopyOnWriteArraySet;
039 import EDU.oswego.cs.dl.util.concurrent.SynchronizedBoolean;
040
041 /**
042 * A helper class for listening for MessageConsumer advisories
043 *
044 * @version $Revision: 1.1.1.1 $
045 */
046 public class ConsumerAdvisor implements MessageListener {
047 private static final Log log = LogFactory.getLog(ConsumerAdvisor.class);
048 private Connection connection;
049 private ActiveMQDestination destination;
050 private Session session;
051 private List listeners = new CopyOnWriteArrayList();
052 private SynchronizedBoolean started = new SynchronizedBoolean(false);
053 private Map activeSubscribers = new ConcurrentHashMap();
054
055 /**
056 * Construct a ConsumerAdvisor
057 *
058 * @param connection
059 * @param destination the destination to listen for Consumer events
060 * @throws JMSException
061 */
062 public ConsumerAdvisor(Connection connection, Destination destination) throws JMSException {
063 this.connection = connection;
064 this.destination = ActiveMQDestination.transformDestination(destination);
065 }
066
067 /**
068 * start listening for advisories
069 *
070 * @throws JMSException
071 */
072 public void start() throws JMSException {
073 if (started.commit(false, true)) {
074 session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
075 MessageConsumer consumer = session.createConsumer(destination.getTopicForConsumerAdvisory());
076 consumer.setMessageListener(this);
077 }
078 }
079
080 /**
081 * stop listening for advisories
082 *
083 * @throws JMSException
084 */
085 public void stop() throws JMSException {
086 if (started.commit(true, false)) {
087 if (session != null) {
088 session.close();
089 }
090 }
091 }
092
093 /**
094 * Add a listener
095 *
096 * @param l
097 */
098 public void addListener(ConsumerAdvisoryEventListener l) {
099 listeners.add(l);
100 }
101
102 /**
103 * Remove a listener
104 *
105 * @param l
106 */
107 public void removeListener(ConsumerAdvisoryEventListener l) {
108 listeners.remove(l);
109 }
110
111 /**
112 * returns true if there is an active subscriber for the destination
113 *
114 * @param destination
115 * @return true if a subscriber for the destination
116 */
117 public boolean isActive(Destination destination) {
118 return activeSubscribers.containsKey(destination);
119 }
120
121 /**
122 * return a set of active ConsumerInfo's for a particular destination
123 * @param destination
124 * @return the set of currently active ConsumerInfo objects
125 */
126 public Set activeConsumers(Destination destination) {
127 Set set = (Set) activeSubscribers.get(destination);
128 return set != null ? set : new CopyOnWriteArraySet();
129 }
130
131 /**
132 * OnMessage() implementation
133 *
134 * @param msg
135 */
136 public void onMessage(Message msg) {
137 if (msg instanceof ObjectMessage) {
138 try {
139 ConsumerInfo info = (ConsumerInfo) ((ObjectMessage) msg).getObject();
140 updateActiveConsumers(info);
141 ConsumerAdvisoryEvent event = new ConsumerAdvisoryEvent(info);
142 fireEvent(event);
143 }
144 catch (JMSException e) {
145 log.error("Failed to process message: " + msg);
146 }
147 }
148 }
149
150 private void fireEvent(ConsumerAdvisoryEvent event) {
151 for (Iterator i = listeners.iterator();i.hasNext();) {
152 ConsumerAdvisoryEventListener l = (ConsumerAdvisoryEventListener) i.next();
153 l.onEvent(event);
154 }
155 }
156
157 private void updateActiveConsumers(ConsumerInfo info) {
158 Set set = (Set) activeSubscribers.get(info.getDestination());
159 if (info.isStarted()) {
160 if (set == null) {
161 set = new CopyOnWriteArraySet();
162 activeSubscribers.put(info.getDestination(), set);
163 }
164 set.add(info);
165 }
166 else {
167 if (set != null) {
168 set.remove(info);
169 if (set.isEmpty()) {
170 activeSubscribers.remove(info.getDestination());
171 }
172 }
173 }
174 }
175 }