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 */
017package org.apache.activemq.advisory;
018
019import java.util.concurrent.atomic.AtomicBoolean;
020import java.util.concurrent.atomic.AtomicInteger;
021
022import javax.jms.Connection;
023import javax.jms.Destination;
024import javax.jms.JMSException;
025import javax.jms.Message;
026import javax.jms.MessageListener;
027import javax.jms.Session;
028
029import org.apache.activemq.ActiveMQMessageConsumer;
030import org.apache.activemq.Service;
031import org.apache.activemq.command.ActiveMQDestination;
032import org.apache.activemq.command.ActiveMQMessage;
033import org.apache.activemq.command.ActiveMQTopic;
034import org.apache.activemq.command.ConsumerId;
035import org.apache.activemq.command.ConsumerInfo;
036import org.apache.activemq.command.RemoveInfo;
037import org.slf4j.Logger;
038import 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 */
046public 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}