Features > Broker Camel Component
Available as of ActiveMQ 5.9
Embedding Apache Camel inside the ActiveMQ broker provides great flexibility for extending the message broker with the integration power of Camel. Apache Camel routes also benefit in that you can avoid the serialization and network costs of connecting to ActiveMQ remotely - if you use the activemq component.
If however, you want to change the behavior of messages flowing through the ActiveMQ message broker itself you will be limited to the shipped set of ActiveMQ broker Interceptors - or develop your own Broker plugin and then introduce that as a jar on to the class path for the ActiveMQ broker. The broker
Camel component makes this even easier. It intercepts messages as they move through the broker itself, allowing them to be modified and manipulated before they are persisted to the message store or delivered to end consumers.
For example by defining a CamelContext to run inside the broker's JVM the broker
component can intercept all messages published to a Topic, say, and publish them to a Queue instead, changing their priority along the way:
<route id="setPriority"> <from uri="broker:topic:test.broker.>"/> <setHeader headerName="JMSPriority"> <constant>9</constant> </setHeader> <to uri="broker:queue:test.broker.component.queue"/> </route>
Notes:
IN
message on the Exchange is a CamelMessage
, but also a JMS Message (messages routed through ActiveMQ from STOMP/MQTT/AMQP etc. are always translated into JMS messages).There is one deliberate caveat though, only intercepted messages can be sent to a broker
component. For example, routing a Camel message from another Component e.g. file
, will result in an error.
Extra classes that have been added to the activemq-broker
package to support the broker
component. They allow the state of the running broker to be interrogated without using JMX. These classes are:
org.apache.activemq.broker.view.MessageBrokerView
- you can retrieve a org.apache.activemq.broker.view.BrokerDestinationView for a particular destination.How to route messages when a destination's queue depth has reached a certain limit:
<camelContext id="camel" trace="false" xmlns="http://camel.apache.org/schema/spring"> <route id="routeAboveQueueLimitTest"> <from uri="broker:queue:test.broker.queue"/> <choice> <when> <spel>#{@destinationView.queueSize >= 100}</spel> <to uri="broker:queue:test.broker.processLater"/> </when> <otherwise> <to uri="broker:queue:test.broker.queue"/> </otherwise> </choice> </route> </camelContext> <bean id="brokerView" class="org.apache.activemq.broker.view.MessageBrokerView"> <constructor-arg value="testBroker"/> </bean> <bean id="destinationView" factory-bean="brokerView" factory-method="getDestinationView"> <constructor-arg value="test.broker.component.route"/> </bean>
This is using the Camel Message Router pattern. Note the use of the Spring expression language spel
in the when
clause.