As follow up to previous posts covering JMS, this post will delve into more depth on Spring's CachingConnectionFactory.

Spring provides two implementations of the javax.jms.ConnectionFactory interface, namely, the SingleConnectionFactory and the CachingConnectionFactory. The SingleConnectionFactory returns as you might expect the same single connection upon all calls to the createConnection() method. This is fine for certain scenarios and applications but the CachingConnectionFactory provides a more performant and scalable solution.

By default, a single session is cached so for a multi threaded application you would set the sessionCacheSize to be a more suitable number although this number wouldn't reflect the true number of sessions cached as this figure refers to the size of cache per session acknowledgement type eg AUTO_ACKNOWLEDGE, CLIENT_ACKNOWLEDGE, DUPS_OK_ACKNOWLEDGE and SESSION_TRANSACTED.

By default, the CachingConnectionFactory will cache the Message Producers and Message Consumers for every session. As an aside the Message Consumers are cached using keys which include the JMS selector so the more fine grained the message filter the more Message Consumers there would be, and Message Consumers aren't closed until the session is closed and removed from the pool. An alternative is to use a Listener Container for consuming messages.

Also to be noted is that on creating a CachingConnectionFactory instance, the reconnect on exception flag is set to be true. This should mean that the onException method on the default ExceptionListener class gets called which will reset the connections. You can also override the default exception listener with your own implementation.

The below snippet of XML shows a simple configuration of a CachingConnectionFactory: 

<bean id="jmsQueueConnectionFactory"
    class="org.springframework.jms.connection.UserCredentialsConnectionFactoryAdapter">
    <property name="targetConnectionFactory" ref="mqConnectionFactory" />
    <property name="username" value="${mq.username}" />
</bean>
 
<bean id="jmsConnectionFactory"
    class="org.springframework.jms.connection.CachingConnectionFactory">
    <property name="targetConnectionFactory" ref="jmsQueueConnectionFactory" />
    <property name="sessionCacheSize" value="50" />
    <property name="exceptionListener" ref="jmsExceptionListener" />
</bean>
 
<bean id="jmsExceptionListener"
    class="com.city81.messaging.MessageMQExceptionListener"">
    <property name="cachingConnectionFactory" ref="jmsConnectionFactory" /">
</bean>