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Chapter 3. JMS Transactions

Abstract

JMS endpoints create special problems when transactions are enabled. Their behavior is effected by the type of transaction manager in use, the caching level in use, and the message exchange pattern in use.
Note

3.1. Configuring the JMS Component

Overview

To enable transactions in a JMS component (thus enabling JMS endpoints to play the role either of a transactional resource or a transactional client), you need to:
  • set the transacted property
  • provide the JMS component with a reference to a suitable transaction manager
In addition, you may want to adjust the JMS component's cache level setting. External transaction managers can impact caching performance.

Camel JMS component configuration

The easiest way to configure a JMS endpoint to participate in transactions is to create a new an instance of a Camel JMS component that has the proper settings. To do so:
  1. Create a bean element that has its class attribute set to org.apache.camel.component.jms.JmsComponent.
    This bean creates an instance of the JMS component.
  2. Set the bean's id attribute to a unique, short, string.
    The id will be used to create route endpoint's that use this JMS component.
  3. Add an empty property child to the bean.
  4. Add a name attribute with the value of configuration to the property element.
  5. Add a ref attribute whose value is the id of a JmsConfiguration bean to the property element.
    The JmsConfiguration bean is used to configure the JMS component.
  6. Create a bean element that has its class attribute set to org.apache.camel.component.jms.JmsConfiguration.
    This bean creates an instance of the JMS component configuration.
  7. Set the bean's id attribute to the value supplied for the ref attribute in Step 5.
  8. Add a property child to the bean to configure the JMS connection factory.
    1. Set the name attribute to connectionFactory.
    2. Set the ref attribute to the id of a bean that configures a JMS connection factory.
  9. Add an empty property child to the bean that specifies the transaction manager the component will use.
    1. Set the name attribute to transactionManager.
    2. Set the ref attribute to the id of a bean that configures transaction manager the endpoint will use.
    See Chapter 2, Selecting a Transaction Manager.
  10. Add an empty property child to the bean that configures the component to participate in transactions.
    1. Set the name attribute to transacted.
    2. Set the value attribute to true.
      The transacted property determines if the endpoint can participate in transactions.
  11. Optionally add an empty property child to the bean to change the default cache level.
    1. Set the name attribute to cacheLevelName.
    2. Set the value attribute to to a valid cache level. For details, see the section called “Cache levels and performance”.
The JmsComponent bean's id specifies the URI prefix used by JMS endpoints that will use the transactional JMS component. For example, in Example 3.1, “JMS Transaction Manager Configuration” the JmsComponent bean's id equals jmstx, so endpoint that use the configured JMS component use the jmstx: prefix.
The JmsConfiguration class supports a large number of other properties, which are essentially identical to the JMS URI options described in chapter "JMS" in "Apache Camel Component Reference".

Cache levels and performance

The settings for JMS cache level can impact performance when you are using transactions. The default cache level is CACHE_AUTO. This default auto detects if an external transaction manager is in use and sets the cache level as follows:
  • CACHE_CONSUMER if only local JMS resources are in use
  • CACHE_NONE if an external transaction manager is in use
If your transaction manager does not require that caching be disabled, you can raise the cache level to improve performance. Consult your transaction manager's documentation to determine what caching level it can support. Then override the default cache level by setting the JMS component's cacheLevelName property to the new cache level.
See chapter "JMS" in "Apache Camel Component Reference" for information on setting the cache level of the JMS component.

Caching with ActiveMQ endpoints

When the transactional resource is ActiveMQ, you can use either CACHE_CONNECTION or CACHE_CONSUMER for local JMS transactions.
CACHE_CONSUMER improves performance significantly, but to avoid losing messages on failover:
  • Do not set a transaction manager, and
  • Set the lazyCreateTransactionManager property to false in your JMS configuration.
For an example route definition using CACHE_CONNECTION, see the section called “Example using CACHE_CONNECTION”. For an example route definition using CACHE_CONSUMER, see the section called “Example using CACHE_CONSUMER”.
Important
Be careful when configuring caching with local transactions. The configurations shown in the section called “Example using CACHE_CONNECTION” and the section called “Example using CACHE_CONSUMER” are believed to be safe (that is, no risk of message loss) for configuring Camel routes where the consumer and producer endpoints both connect to the same broker instance. For other configurations involving local transactions, it is generally safer to disable caching (CACHE_NONE).

Example using CACHE_CONSUMER

This route definition routes messages between two destinations on the same broker using local transactions. Not setting a transaction manager makes Spring use only one JMS session and one transaction. The Camel route is fully transacted because the Camel consumer and producer endpoints are transacted. 
<camel:camelContext trace="false" id="My.impl.CamelContext">
    <camel:route id="Queue2Backend">
        <camel:from uri="activemq:queue:TEST.amq.failover.inputQueue" /> 
        <camel:log message="Sending message to backend..."/>
        <camel:to uri="activemq:queue:TEST.amq.failover.backendQueue" />
    </camel:route>
</camel:camelContext>

<bean id="jmsConectionFactory" class="org.apache.activemq.pool.PooledConnectionFactory" destroy-method="stop">
    <property name="connectionFactory">
        <bean id="jmsConnectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
           <property name="brokerURL" value="failover:(tcp://localhost:61616?wireFormat.
                  tightEncodingEnabled=false)?initialReconnectDelay=10000&useExponentialBackOff=false
                  &maxReconnectDelay=10000"/>
           <property name="userName" value="admin"/>
           <property name="password" value="admin"/>
       </bean>
    </property>
    <property name="maxConnections" value="1"/>
</bean>

<bean id="jmsConfig" class="org.apache.camel.component.jms.JmsConfiguration">
    <property name="connectionFactory" ref="jmsConectionFactory"/>
    <property name="lazyCreateTransactionManager" value="false"/>
    <property name="transacted" value="true"/>
    <property name="concurrentConsumers" value="1"/>
    <property name="cacheLevelName" value="CACHE_CONSUMER"/>
</bean>

<bean id="activemq" class="org.apache.activemq.camel.component.ActiveMQComponent">
    <property name="configuration" ref="jmsConfig"/>
</bean>

Example using CACHE_CONNECTION

Example 3.1, “JMS Transaction Manager Configuration” shows the configuration of a JMS component, jmstx that supports Spring transactions. The JMS component is layered over an embedded instance of Apache ActiveMQ and the transaction manager is an instance of JmsTransactionManager.

Example 3.1. JMS Transaction Manager Configuration

<beans xmlns="http://www.springframework.org/schema/beans" 
       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-2.5.xsd
       http://camel.apache.org/schema/spring http://camel.apache.org/schema/spring/camel-spring.xsd">
  ...
  <bean id="jmstx" class="org.apache.camel.component.jms.JmsComponent"> 
    <property name="configuration" ref="jmsConfig" /> 
  </bean> 

  <bean id="jmsConfig" class="org.apache.camel.component.jms.JmsConfiguration"> 
      <property name="connectionFactory" ref="jmsConnectionFactory"/> 
      <property name="transactionManager" ref="jmsTransactionManager"/> 
      <property name="transacted" value="true"/>
      <property name="cacheLevelName" value="CACHE_CONNECTION"/>
  </bean> 

  <bean id="jmsTransactionManager" class="org.springframework.jms.connection.JmsTransactionManager">
    <property name="connectionFactory" ref="jmsConnectionFactory" />
  </bean>
  
  <bean id="jmsConnectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
    <property name="brokerURL" value="vm://broker1?brokerConfig=xbean:tutorial/activemq.xml"/>
  </bean>

</beans>
To use this JMS component in a route you would use the URI prefix jmstx: as shown in Example 3.2, “URI for Using Transacted JMS Endpoint”.

Example 3.2. URI for Using Transacted JMS Endpoint

from("jmstx:queue:rawStockQuotes")
    .process(myFormatter)
    .to("jmstx:queue:formattedStockQuotes");
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