/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.activemq.advisory;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import javax.jms.Connection;
import javax.jms.Destination;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageListener;
import javax.jms.Session;
import org.apache.activemq.Service;
import org.apache.activemq.command.ActiveMQDestination;
import org.apache.activemq.command.ActiveMQMessage;
import org.apache.activemq.command.ActiveMQTopic;
import org.apache.activemq.command.ConsumerId;
import org.apache.activemq.command.ConsumerInfo;
import org.apache.activemq.command.RemoveInfo;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* An object which can be used to listen to the number of active consumers
* available on a given destination.
*
* @version $Revision: 564271 $
*/
public class ConsumerEventSource implements Service, MessageListener {
private static final Log LOG = LogFactory.getLog(ConsumerEventSource.class);
private final Connection connection;
private final ActiveMQDestination destination;
private ConsumerListener listener;
private AtomicBoolean started = new AtomicBoolean(false);
private AtomicInteger consumerCount = new AtomicInteger();
private Session session;
private MessageConsumer consumer;
public ConsumerEventSource(Connection connection, Destination destination) throws JMSException {
this.connection = connection;
this.destination = ActiveMQDestination.transform(destination);
}
public void setConsumerListener(ConsumerListener listener) {
this.listener = listener;
}
public void start() throws Exception {
if (started.compareAndSet(false, true)) {
session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
ActiveMQTopic advisoryTopic = AdvisorySupport.getConsumerAdvisoryTopic(destination);
consumer = session.createConsumer(advisoryTopic);
consumer.setMessageListener(this);
}
}
public void stop() throws Exception {
if (started.compareAndSet(true, false)) {
if (session != null) {
session.close();
}
}
}
public void onMessage(Message message) {
if (message instanceof ActiveMQMessage) {
ActiveMQMessage activeMessage = (ActiveMQMessage)message;
Object command = activeMessage.getDataStructure();
int count = 0;
if (command instanceof ConsumerInfo) {
count = consumerCount.incrementAndGet();
count = extractConsumerCountFromMessage(message, count);
fireConsumerEvent(new ConsumerStartedEvent(this, destination, (ConsumerInfo)command, count));
} else if (command instanceof RemoveInfo) {
RemoveInfo removeInfo = (RemoveInfo)command;
if (removeInfo.isConsumerRemove()) {
count = consumerCount.decrementAndGet();
count = extractConsumerCountFromMessage(message, count);
fireConsumerEvent(new ConsumerStoppedEvent(this, destination, (ConsumerId)removeInfo.getObjectId(), count));
}
} else {
LOG.warn("Unknown command: " + command);
}
} else {
LOG.warn("Unknown message type: " + message + ". Message ignored");
}
}
/**
* Lets rely by default on the broker telling us what the consumer count is
* as it can ensure that we are up to date at all times and have not
* received messages out of order etc.
*/
protected int extractConsumerCountFromMessage(Message message, int count) {
try {
Object value = message.getObjectProperty("consumerCount");
if (value instanceof Number) {
Number n = (Number)value;
return n.intValue();
}
LOG.warn("No consumerCount header available on the message: " + message);
} catch (Exception e) {
LOG.warn("Failed to extract consumerCount from message: " + message + ".Reason: " + e, e);
}
return count;
}
protected void fireConsumerEvent(ConsumerEvent event) {
if (listener != null) {
listener.onConsumerEvent(event);
}
}
}