Introducing Spring Framework

Chapter 16 ■ Messaging with Your Spring Application
public void send(Document document){
}
}
rabbitTemplate.convertAndSend(EXCHANGE,document.getType().getExtension(),document);
Listing 16-1 shows the new producer. You can see that you are using a variable named Exchange with the value
of mydocuments, and you are still using the RabbitTemplate, but now you are using a different method to publish the
document. If you remember in Chapter 11, I never mentioned any exchange; you used a Message object and you
converted the document into an XML format. But wait! What does that exchange do?
RabbitMQ: Exchanges, Bindings, and Queues
Let’s review the basic RabbitMQ messaging architecture. RabbitMQ is based on the AMQP (Advance Message
Queue Protocol) and it offers routing capabilities through exchanges. You can see an exchange as an entry point for
the message, and the exchange is in charge of delivering the message to the correct queue based on the routing key
provided by the bindings. Figure 16-1 shows the basic architecture based on the direct exchange.
Figure 16-1. The RabbitMQ Direct Exchange Routes the Messages Based on the Routing Key to the Correct Queue
As you can see in Figure 16-1, a producer sends a message to the mydocuments exchange; this message
has a routing key of either .pdf or .txt. Then, based on the binding, the exchange will put the message in the
corresponding queue, either docs-pdf or docs-txt.
RabbitMQ also has Topic, Headers, and Fanout exchanges, and each one offers different routing mechanisms. In
Listing 16-1, you are using the convertAndSend method that accepts three parameters. The first parameter is the name of
the exchange, in this case, mydocuments; the second parameter is the routing key, in this case the document’s extension
(either .pdf, .txt, or .url); and the last parameter is the document itself. The convertAndSend method is one of several
methods that allows you to publish using the org.springframework.amqp.rabbit.core.RabbitTemplate class.
This class is part of the Spring-AQMP extension. You can take a look at the Spring-AMQP extension to explore more
about the API at http://docs.spring.io/spring-amqp/docs/latest-ga/api/.
As you can see in Figure 16-1, there is a queue per extension, so you need to create a consumer for every queue;
in your case, it will be one consumer for the PDF, one for the text, and one for the web documents. In other words, a
consumer will be listening from the docs-pdf queue, another consumer will be listening from the docs-txt queue, and
the last consumer will be listening from the docs-web queue. Listings 16-2, 16-3, 16-4, and 16-5 show your consumers.
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