1 Introduction

Examples

The following are some simple examples to give you a feel for the plugin.

Service Queue Listeners

class ListeningService {
    static exposes = ['jms']
    def onMessage(message) {
        assert message == 1
    }
}

class SomeController {
    def jmsService
    def someAction = {
        jmsService.send(service: 'listening', 1)
    }
}

Service Method Queue Listeners

import grails.plugin.jms.Queue
class ListeningService {
    static exposes = ['jms']
    @Queue
    def receive(message) {
        assert message == 1
    }
}

class SomeController {
    def jmsService
    def someAction = {
        jmsService.send(service: 'listening', method: 'receive', 1)
    }
}

Topic Listeners

import grails.plugin.jms.Subscriber
class ListeningService {
    static exposes = ['jms']
    @Subscriber
    def newMessages(message) {
        assert message == 1
    }
}

class SomeController {
    def jmsService
    def someAction = {
        jmsService.send(topic: 'newMessages', 1)
    }
}

Post Processing Messages

import javax.jms.Message
class SomeController {
    def jmsService
    def someAction = {
        jmsService.send(service: 'initial', 1) { Message msg ->
            msg.JMSReplyTo = createDestination(service: 'reply')
            msg
        }
    }
}

1.1 Spring JMS

There are some core Spring JMS concepts that you should at least be aware of.

JmsTemplate

Spring provides JmsTemplate which is what this plugin uses to send messages.

MessageConverter

The MessageConverter abstraction conveniently allows pluggable message conversion. By default, this plugin uses Spring's SimpleMessageConverter which handles 'standard' message payloads and JMS Message types.

MessageListenerContainer

A listener container polls a JMS destination for messages. Each listener (i.e. each service method that receives JMS messages) has it's own listener container.

This plugin uses the DefaultMessageListenerContainer implementation.

MessageListenerAdapter

A listener adapter connects a listener container to the actual destination of the message. It handles message conversion amongst other things.

By default, this plugin uses a MessageListenerAdapter subclass that is Grails aware and sets up the necessary Grails environment for listener methods (e.g. Hibernate session).