Review

In the previous section, we created the core Event management system and utilized the Spring Data JPA project to simplify data access. We've also added AJAX functionality to make the application responsive. In this section, we will integrate RabbitMQ and messaging in general.

Where am I?

Messaging Support

Our application is capable of broadcasting events as simple text messages. These messages are CRUD actions and exceptions that arise during the lifetime of the application. This means if a user performs an add, edit, delete, or get these actions will be published to a message broker. If there are any exceptions, we will also publish them.

Why do we need to publish these events? First, it helps us study and explore RabbitMQ messaging. Second, we can have a third-party application whose sole purpose is to handle these messages for intensive statistical analysis. Third, it allows us to monitor in real-time and check the status of our application instantaneously.

If you're unfamiliar with messaging and its benefits, I suggest visiting the following links:

We'll divide this page into four sections:

B. Messaging Support
- B1. Aspect
- B2. Configuration
- B3. Controller
- B4. View

B1. Aspect

We will publish CRUD operations as simple messages. It's like logging except we send the logs to a message broker. Usually we would add this feature across existing classes. Unfortunately, this leads to "scattering" and " tangling" of code. No doubt--it's a crosscutting concern. We have the same scenario when added the logging feature earlier (See A5. Crosscutting Concerns section earlier).

We have created an Aspect, EventRabbitAspect.java, to solve this concern. To send messages, we use the AmqpTemplate where we pass the exchange, routing key, and the message. Since we want to publish messages as they are called and also errors as they happened, we use @Around to capture these events. The proceeding code is a variation of the original tutorial Chatting in the Cloud: Part 1 by Mark Fisher (http://blog.springsource.com/2011/08/16/chatting-in-the-cloud-part-1/)

EventRabbitAspect.java

In order for Spring to recognize this aspect, make sure to declare the following element in your XML configuration (we've done this in the trace-context.xml):

B2. Configuration

After declaring the Aspect, we now declare and configure the RabbitMQ and Spring AMQP specific settings. In fact, you will soon discover that most of the work with Spring AMQP is configuration-related: declaration of queues, bindings, exchanges, and connection settings.

We've declared two queues: eventQueue for normal events, and errorQueue for errors. We have a single exchange, eventExchange where we declare the bindings for the two queues.

In order to send messages to the eventQueue, we set the routing key to event.general.*. Likewise, to send messages to the errorQueue, we set the routing key to event.error.*. For a tutorial on these concepts, please visit the official examples at http://www.rabbitmq.com/getstarted.html

spring-rabbit.xml

B3. Controller

After configuring RabbitMQ and Spring AMQP, we declare a controller, aptly named MonitorController. It's main purpose is to handle monitoring requests. This controller is based on Chatting in the Cloud: Part 1 blog by Mark Fisher (http://blog.springsource.com/2011/08/16/chatting-in-the-cloud-part-1/).

MonitorController.java

B4. View

We have two JSP pages event-monitor-page.jsp and error-monitor-page.jsp for event and error views respectively. We've utilized AJAX to pull information from the application. Again, this is based on Chatting in the Cloud: Part 1 blog by Mark Fisher (http://blog.springsource.com/2011/08/16/chatting-in-the-cloud-part-1/).

event-monitor-page.jsp

error-monitor-page.jsp