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This tutorial was kindly donated to Apache Camel by Martin Gilday.
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This tutorial aims to guide the reader through the stages of creating a project which uses Camel to facilitate the routing of messages from a JMS queue to a Spring service. The route works in a synchronous fashion returning a response to the client.toc
Prerequisites
This tutorial uses Maven to setup the Camel project and for dependencies for artifacts.
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Component | Description |
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We use Apache ActiveMQ as the JMS broker on the Server side | |
We use the bean binding to easily route the messages to our business service. This is a very powerful component in Camel. | |
In the AOP enabled Server we store audit trails as files. | |
Used for the JMS messaging |
Create the Camel Project
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For the purposes of the tutorial a single Maven project will be used for both the client and server. Ideally you would break your application down into the appropriate components.
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Update the POM with Dependencies
First we need to have dependencies for the core Camel jars, spring, jms components, and finally ActiveMQ as the message broker. Wiki Markup Wiki Markup
Writing the Server
Create the Spring Service
For this example the Spring service (our business service) on the server will be a simple multiplier which trebles in the received value. Wiki Markup Wiki Markup
Define the Camel Routes
{snippet Wiki Markup
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The Spring config file is placed under META-INF/spring
as this is the default location used by the Camel Maven Plugin, which we will later use to run our server.
First we need to do the standard scheme declarations in the top. In the camel-server.xml we are using spring beans as the default bean: namespace and springs context:. For configuring ActiveMQ we use broker: and for Camel we of course have camel:. Notice that we don't use version numbers for the camel-spring schema. At runtime the schema is resolved in the Camel bundle. If we use a specific version number such as 1.4 then its IDE friendly as it would be able to import it and provide smart completion etc. See Xml Reference for further details. Wiki Markup Wiki Markup
Notice that we also have enabled the JMXAgent so we will be able to introspect the Camel Server with a JMX Console. Wiki Markup Wiki Markup {snippet:id: Wiki Markup from="jmsbroker:queue:numbers).to("multiplier");
We use the vm protocol to connect to the ActiveMQ server as its embedded in this application.
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We will initially create a client by directly using ProducerTemplate
. We will later create a client which uses Spring remoting to hide the fact that messaging is being used. Wiki Markup Wiki Markup Wiki Markup
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And the CamelClient source code: Wiki Markup ProducerTemplate
is retrieved from a Spring ApplicationContext
and used to manually place a message on the "numbers" JMS queue. The requestBody
method will use the exchange pattern InOut, which states that the call should be synchronous, and that the caller expects a response.
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Spring Remoting "eases the development of remote-enabled services". It does this by allowing you to invoke remote services through your regular Java interface, masking that a remote service is being called. Wiki Markup
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And the Java client source code: Wiki Markup
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Okay enough talk, show me the code! Wiki Markup "mina:tcp://localhost:61610"
then its just a matter of getting hold of this endpoint instead of the JMS and all the rest of the java code is exactly the same.
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The Camel Maven Plugin allows you to run your Camel routes directly from Maven. This negates the need to create a host application, as we did with Camel server, simply to start up the container. This can be very useful during development to get Camel routes running quickly.
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All that is required is a new plugin definition in your Maven POM. As we have already placed our Camel config in the default location (camel-server.xml has been placed in META-INF/spring/) we do not need to tell the plugin where the route definitions are located. Simply run mvn camel:run
.
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Camel has extensive support for JMX and allows us to inspect the Camel Server at runtime. As we have enabled the JMXAgent in our tutorial we can fire up the jconsole and connect to the following service URI: service:jmx:rmi:///jndi/rmi://localhost:1099/jmxrmi/camel
. Notice that Camel will log at INFO level the JMX Connector URI:
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In the screenshot below we can see the route and its performance metrics:
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