Question

I am working on a web project that uses Spring and RabbitMQ. This is a basic system with a Master node sending tasks to Slave nodes (using a direct exchange) and Slave nodes responding to the Master using a simple queue.

New slaves may come and go at any time so they use anonymous queues. There can also be multiple Master nodes, in which case each of them will have their own reply queue. When a Master sends a task to slaves, the task contains the name of the reply queue of the master who sent it. Sending messages is done using AmqpTemplate.

I’m configuring all of this using XML, here’s what I’ve got so far:

For the Slave:

<!-- Message listener -->
<bean id="taskListener" class="tgi.docgen.amqp.TypedListener" />
  <bean id="slave" class="tgi.docgen.node.Slave" />
    <bean id="handler" class="tgi.docgen.task.TaskHandler" />

<!-- Rabbit infrastructure -->
<!-- Slave reading queue, bound to the exchange -->
<rabbit:queue id="receiveQueue" auto-delete="true" durable="false" />

<!-- Master -> Slave exchange -->
<rabbit:direct-exchange name="docgenExchange" auto-delete="true" durable="false">   
    <rabbit:bindings>
        <rabbit:binding queue="receiveQueue" />
    </rabbit:bindings>
</rabbit:direct-exchange>

<!-- taskListener bean listens to the queue -->
<rabbit:listener-container connection-factory="rabbitFactory">
    <rabbit:listener queues="receiveQueue" ref="taskListener" />
</rabbit:listener-container>

For the Master:

<!-- Message listener -->
<bean id="taskListener" class="tgi.docgen.amqp.TypedListener" />
  <bean id="master" class="tgi.docgen.node.Master">
      <property name="docgenExchange" value="???" />
      <property name="receiveQueue" value="???" />
  </bean>

<!-- Rabbit infrastructure -->
<!-- Anonymous reception queue -->
<rabbit:queue id="receiveQueue" auto-delete="true" durable="false" />

<!-- Master -> Slave exchange -->
<rabbit:direct-exchange name="docgenExchange" auto-delete="true" durable="false" />

<!-- taskListener listens to reception queue -->
<rabbit:listener-container connection-factory="rabbitFactory">
    <rabbit:listener queues="receiveQueue" ref="taskListener" />
</rabbit:listener-container>

Here’s what I want to know

1) how do I avoid repeating the name of the exchange in both XML config files ? The Master project depends on the Slave project so I can easily share configuration between them, but I don’t see how I can extract the exchange name and use it in both files.

2) As I’ve said, the Master will send tasks to the exchange, and must write the name of its reply queue in the tasks. How can I inject the name of the queue and the exchange in the Master bean ? That is: how can i replace the two ??? with respectively “docgenExchange” and the generated name of the anonymous reply queue in my config file above ?

Answer 1

That’s not Spring Integration 2?

Anyway, I’ve made a “proof of concept” for myself a few days ago doing stuff exactly what you want to archive. See at https://github.com/knalli/task-worker

Regarding to your first question: Well, it depends. It depends what do you exactly want. I see no problem to configure in both projects — project master and project slave — the name of the central queue. Of course, this should not be hardcoded but a configuration option. And you can provide both running programs the same external properties which will used as a Property Placeholder Bean within the Spring Configuration Context.

The second is a little bit weird: Perhaps you had an old example or this is Spring Ingegration 1.x.. I don’t know. Anyway: You don’t need to provide a reply name. Because this will be handled automatically by Spring Integration for you if you use the AMPQ Gateway Beans.

I cite a port of the configuration of the Inbound AMQP Gateway configuration of my daemon (this is your “slave”):

<int-amqp:inbound-gateway 
    connection-factory="connectionFactory" 
    request-channel="requestChannel"
    reply-channel="replyChannel" 
    error-channel="errorChannel"
    queue-names="${rabbitmq.queue}"/>

Each of the mentioned channels — requestChannel, replyChannel, errorChannel — are only registered in the Spring Integration Context via a simple

 <int:channel id="requestChannel"/>

For AMQP — meaning Message Broker configuration — there is no need for more configuration parts except the <rabbit:queue> item.

Furthermore, I’d use Java annotations to wire the messages to services interfaces (@Gateway) and service classes (@ServiceActivator). This reduces the configuration a lot.