Something that took me a long way to really understand. And I only got there by debugging through the low level Spring and ActiveMQ code.
There are various articles out there that warn you about using JmsTemplate for producing messages outside any container. A runtime container will usually pool your JMS resources (connection, session and producer), but when using JmsTemplate in a standalone application, no pooling is there per se. The JmsTemplate is certainly not responsible for pooling resources.
I have seen a number of applications that use JmsTemplate outside of any applicaton server container for producing messages. It seems to be more popular than using the plain JMS APIs. No wonder as Spring JMS provides such a nice layer of abstraction that shields all the low level JMS code, just like this snippet:
ConnectionFactory cf2 = new ConnectionFactory("tcp://localhost:61616");
JmsTemplate template = new JmsTemplate(cf2);
template.send("MyQueue", new MessageCreator() {
public Message createMessage(Session session)
throws JMSException {
TextMessage tm = session.createTextMessage();
tm.setText("A new message");
return tm;
}
});
However something that is easily forgotten is that this code will create a new JMS connection, consumer and producer for each call to JmsTemplate.send(). Creating these JMS objects are expensive operations and according to the JMS spec these resources are meant to be re-used and not re-created for every message. Performance is going to suffer dramatically when they are not re-used.
That’s pretty clear to most developers but very easily forgotten.
So what is really needed in order to pool all these JMS resources when sending messages with JmsTemplate? I personally was confused whether I need to configure some Jencks container in order to have the JMS resources pooled or could I use plain ActiveMQ connection factories and how does the configuration need to look like? The various documentations I found only added to that confusion.
The answer is pretty simple: All that is needed is to use the org.apache.activemq.pool.PooledConnectionFactory. It will serve JMS connections from its internal pool and wrap them in a PooledConnection instance. The purpose of the PooledConnection is to also pool any JMS sessions and producers that get created. The pool can be configured of course.
For using the JmsTemplate there is no need to configure any containers like Jencks and others. Also see http://activemq.apache.org/jmstemplate-gotchas.html for some additional information on this topic.
The following simple and complete Spring configuration is enough:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">
<bean id="connectionFactory"
class="org.apache.activemq.pool.PooledConnectionFactory">
<constructor-arg value="failover:(tcp://localhost:61616)"/>
</bean>
<bean id="jmsTemplate"
class="org.springframework.jms.core.JmsTemplate">
<constructor-arg ref="connectionFactory"/>
<property name="sessionTransacted" value="false"/>
<property name="receiveTimeout" value="5000"/>
</bean>
</beans>
It pre-configures the JmsTemplate to use the ActiveMQ PooledConnectionFactory so it can be used straight away in a Java program:
package org.apache.activemq.test.jmstemplate;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.Session;
import javax.jms.TextMessage;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.jms.core.JmsTemplate;
import org.springframework.jms.core.MessageCreator;
public class JmsTemplateTest {
public static void main(String[] args) throws Exception {
ApplicationContext ctx = new ClassPathXmlApplicationContext(
"JmsTemplateTest-context.xml");
JmsTemplate template = (JmsTemplate) ctx.getBean("jmsTemplate");
for(int i=0; i<10; i++) {
template.send("MyQueue", new MessageCreator() {
public Message createMessage(Session session)
throws JMSException {
TextMessage tm = session.createTextMessage();
tm.setText("This is a test message");
return tm;
}
});
}
System.exit(1);
}
}
A Maven based test case is provided. It can be checked out using
svn checkout http://abloggerscode.googlecode.com/svn/trunk/JmsTemplateDemo
Once checked out, follow the instructions in README.txt.
Be careful when using Springs SingleConnectionFactory. It does re-use the underlying JMS connection but it does not re-use the JMS session and producer when configured to internally work with the ActiveMQConnectionFactory!
