Grails 2.0

Messaging Integration

Grails needs to provide a universal messaging system not just something specific to e-mail, although this is clearly important. Rather than introducing two concepts that are essentially the same (email and messaging) they need to be unified into a single concept to avoid duplication of effort.

Asynchronous messaging essentially defines the concept of a topic and subscribers and publishers to a topic.

Publishers

A publisher is simply a groovy class that follows the convention *Publisher. By default the first part of the name defines the topic it is publishing to:

class ExamplePublisher {
	def sendX() {
		return [modelObject:"blah"]
	}
}

Here we're publishing to an "example" topic and the sendX() method creates a model that will be used in the sending. In the case of e-mail the sendX method will delegate the model to a views/email/x.gsp view to create the e-mail content itself. Alternatively in JMS this model will be passed in the messaging context to the subscriber.

If a publisher needs to send a message to another topic it can do:

def sendXToTopicName() {
         return [mnodelObject:"blah"]
     }

The topic that a publisher publishes to by default can also be changed using the "topic" property:

def topic = "another"

Subscribers

class ExampleSubscriber {
    def onMessage(ctx) {
    }
}

Topics

class ApplicationConfig {
	def topics =  {
              example(type:EMAIL) {
                    server = "localhost"
                    port = 3434
                    // etc
              }
        }
}