As you know I'm open-sourcing and completely overhauling my PhD system. One of my goals was to replace internal JMS queues with AMQP. Today I'll show you how I did it and why I was forced to change RabbitMQ to Apache Qpid.

AMQP

In short. AMQP is an open standard application layer protocol for message-oriented middleware. The most important feature is that AMQP is a wire-level protocol and is interoperable by design. JMS is just an API. Altough JMS brokers can be used in .NET applications (see my post: ActiveMQ and .NET combined!), the whole JMS specification does not guarantee interoperability. Also, the AMQP standard is by design more flexible and powerful (e.g., supports two-way communication by design) - they simply learnt from JMS mistakes :).

Oh, forgot to mention. The AMQP was originally developed by banks :) so I don't have to say that AMQP is secure, fault-tolerant, and so on.

RabbitMQ

RabbitMQ is the most mature AMQP broker. RabbitMQ is written in Erlang so you have to download that first (RabbitMQ Windows installer does it for you). Download it from here: http://www.rabbitmq.com/.

I also recommend installing the web management console. From Rabbit's sbin directory execute:

rabbitmq-plugins enable rabbitmq_management

If you're on Windows and you installed a Rabbit service you have to restart it.

That's it.

Spring

Well, it turned out that VMware bought RabbitMQ and SpringSource developers are now developing it. Given this fact, you shouldn't be surprised that Spring - RabbitMQ integration is childishly simple.

Add spring-rabbit dependency to your Maven project, and then in Spring configuration paste the following:

<rabbit:connection-factory id="connectionFactory" />
<rabbit:template connection-factory="connectionFactory" id="amqpTemplate" routing-key="myqueue" />
<rabbit:admin connection-factory="connectionFactory" />
<rabbit:queue name="myqueue" />

The default configuration assumes that RabbitMQ is running on a local server using the default port and default credentials (guest/guest). Of course all these settings are configurable.

To sent a message to "myqueue" queue, just inject an instance of AmqpTemplate into your service and send the message. An example would be:

@Service
public class HomeController {
    @Autowired
    private AmqpTemplate amqpTemplate;
    public void sendMessage(Bundle bundle) throws IOException {       
        byte[] body = IOUtils.toByteArray(bundle.getInputStream());
        MessageProperties messageProperties = new MessageProperties();
        messageProperties.setContentType(bundle.getContentType());
        messageProperties.setContentLength(bundle.getSize());
        messageProperties.setTimestamp(new Date());
        messageProperties.setDeliveryMode(MessageDeliveryMode.PERSISTENT);
        Message message = new Message(body, messageProperties);
        amqpTemplate.send(message);
    }
}

You can open the web console http://localhost:55672/mgmt/ and see 1 message in "myqueue" queue.

Apache Camel

To read a message from Apache Camel you first have to add camel-amqp dependency to your POM. Then just copy and paste the following route definition:

<camelContext xmlns="http://camel.apache.org/schema/spring">
 <route>
  <from uri="amqp:queue:myqueue" />
  <to uri="log:Message" />
 </route>
</camelContext>

Run the route by executing mvn:camel-run and... you'll see an error.

Making a long story short, Apache Camel 2.9.0 doesn't work with RabbitMQ. This is because the camel-amqp component is using the Apache Qpid client under the hood. The current Qpid version is 0.14, but Qpid guys forgot to upload new jars to the Maven public repo. Thus camel-amqp is still using Qpid 0.12 whose client doesn't seem to negotiate protocols. Even if you exclude qpid-commons and qpid-client dependencies and explicitly add Qpid 0.14 ones (download them and install in your local repo) there will be an exception thrown from the camel-amqp component as there is no longer a default ConnectionFactory constructor.

Thus I was forced to install Qpid.

Qpid

I downloaded the Java server and simply ran it. There is no web management console, but that's OK. You can use JConsole for JMX.

Spring AMQP and Qpid

In order to make Spring AMQP work with Qpid copy and paste the following configuration:

<camelContext xmlns="http://camel.apache.org/schema/spring">
 <route>
  <from uri="amqp:queue:queue" />
  <to uri="log:Message" />
 </route>
</camelContext>

<bean id="amqp" class="org.apache.camel.component.amqp.AMQPComponent">
 <property name="connectionFactory" ref="amqConnectionFactory" />
</bean>

<bean id="amqConnectionFactory" class="org.apache.qpid.client.AMQConnectionFactory">
 <property name="host" value="localhost" />
 <property name="port" value="5672" />
 <property name="defaultUsername" value="guest" />
 <property name="defaultPassword" value="guest" />
 <property name="virtualPath" value="/development" />
</bean>

As you can see in the above snippet I explicitly created AMPQComponent with connectionFactory set to Apache Qpid AMQConnectionFactory object.

Source code and working example

This solution is a part of the Qualitas project. I use Spring MVC to handle uploads of business processes bundles (e.g., zipped archive of a WS-BPEL process) and send it to an AMQP queue. Then Apache Camel consumes the message, does additional processing of the bundle, and installs it on a remote business process execution engine.

The projects you are most interested in are:

• qualitas-webapp (Spring MVC sending messages to AMQP)
• qualitas-internall-installation (Apache Camel route consuming messages from AMQP)

To check out 0.0.2-SNAPSHOT tag from here: http://code.google.com/p/qualitas/source/browse/.

Qualitas

Read more about Qualitas project here: http://code.google.com/p/qualitas/. Happy to welcome new developers on board!

cheers,
Łukasz