001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  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    package org.apache.activemq.advisory;
018    
019    import java.util.concurrent.atomic.AtomicBoolean;
020    import java.util.concurrent.atomic.AtomicInteger;
021    
022    import javax.jms.Connection;
023    import javax.jms.Destination;
024    import javax.jms.JMSException;
025    import javax.jms.Message;
026    import javax.jms.MessageListener;
027    import javax.jms.Session;
028    
029    import org.apache.activemq.ActiveMQMessageConsumer;
030    import org.apache.activemq.Service;
031    import org.apache.activemq.command.ActiveMQDestination;
032    import org.apache.activemq.command.ActiveMQMessage;
033    import org.apache.activemq.command.ActiveMQTopic;
034    import org.apache.activemq.command.ConsumerId;
035    import org.apache.activemq.command.ConsumerInfo;
036    import org.apache.activemq.command.RemoveInfo;
037    import org.slf4j.Logger;
038    import org.slf4j.LoggerFactory;
039    
040    /**
041     * An object which can be used to listen to the number of active consumers
042     * available on a given destination.
043     * 
044     * 
045     */
046    public class ConsumerEventSource implements Service, MessageListener {
047        private static final Logger LOG = LoggerFactory.getLogger(ConsumerEventSource.class);
048    
049        private final Connection connection;
050        private final ActiveMQDestination destination;
051        private ConsumerListener listener;
052        private AtomicBoolean started = new AtomicBoolean(false);
053        private AtomicInteger consumerCount = new AtomicInteger();
054        private Session session;
055        private ActiveMQMessageConsumer consumer;
056    
057        public ConsumerEventSource(Connection connection, Destination destination) throws JMSException {
058            this.connection = connection;
059            this.destination = ActiveMQDestination.transform(destination);
060        }
061    
062        public void setConsumerListener(ConsumerListener listener) {
063            this.listener = listener;
064        }
065        
066        public String getConsumerId() {
067            return consumer != null ? consumer.getConsumerId().toString() : "NOT_SET";
068        }
069    
070        public void start() throws Exception {
071            if (started.compareAndSet(false, true)) {
072                session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
073                ActiveMQTopic advisoryTopic = AdvisorySupport.getConsumerAdvisoryTopic(destination);
074                consumer = (ActiveMQMessageConsumer) session.createConsumer(advisoryTopic);
075                consumer.setMessageListener(this);
076            }
077        }
078    
079        public void stop() throws Exception {
080            if (started.compareAndSet(true, false)) {
081                if (session != null) {
082                    session.close();
083                }
084            }
085        }
086    
087        public void onMessage(Message message) {
088            if (message instanceof ActiveMQMessage) {
089                ActiveMQMessage activeMessage = (ActiveMQMessage)message;
090                Object command = activeMessage.getDataStructure();
091                int count = 0;
092                if (command instanceof ConsumerInfo) {
093                    count = consumerCount.incrementAndGet();
094                    count = extractConsumerCountFromMessage(message, count);
095                    fireConsumerEvent(new ConsumerStartedEvent(this, destination, (ConsumerInfo)command, count));
096                } else if (command instanceof RemoveInfo) {
097                    RemoveInfo removeInfo = (RemoveInfo)command;
098                    if (removeInfo.isConsumerRemove()) {
099                        count = consumerCount.decrementAndGet();
100                        count = extractConsumerCountFromMessage(message, count);
101                        fireConsumerEvent(new ConsumerStoppedEvent(this, destination, (ConsumerId)removeInfo.getObjectId(), count));
102                    }
103                } else {
104                    LOG.warn("Unknown command: " + command);
105                }
106            } else {
107                LOG.warn("Unknown message type: " + message + ". Message ignored");
108            }
109        }
110    
111        /**
112         * Lets rely by default on the broker telling us what the consumer count is
113         * as it can ensure that we are up to date at all times and have not
114         * received messages out of order etc.
115         */
116        protected int extractConsumerCountFromMessage(Message message, int count) {
117            try {
118                Object value = message.getObjectProperty("consumerCount");
119                if (value instanceof Number) {
120                    Number n = (Number)value;
121                    return n.intValue();
122                }
123                LOG.warn("No consumerCount header available on the message: " + message);
124            } catch (Exception e) {
125                LOG.warn("Failed to extract consumerCount from message: " + message + ".Reason: " + e, e);
126            }
127            return count;
128        }
129    
130        protected void fireConsumerEvent(ConsumerEvent event) {
131            if (listener != null) {
132                listener.onConsumerEvent(event);
133            }
134        }
135    
136    }