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Following a question onto my post Grails Service, JMS and an MDB, I was amused and pleased to find that the grails site for the JMS Plugin had been updated and included much of my post. Right down to the xfire reference, setting up Apache ActiveMQ and my service name typo… Sample was meant to be Simple. Unfortunately no citation, though there was quite a bit of other information added too.

Thomas’ question got me to thinking about publish subscribe as opposed to point to point and how that might be set up using Grails.

No changes were needed to the Apache ActiveMQ set up or the spring configuration in the grails app. I simply added another service to the mix.

class SampleTopicService {
    static expose = ['jms']
    static pubSub = true
    static destination = 'test/topic'

    def onMessage(messageObject) {
       println "GOT PUBLISHED MESSAGE: $messageObject"
    }

}

The destination bit was a little allusive at first. Without it or trying the static “topic” results in the default configuration whereby the service name “sampleTopic” is used for the destination (topic or queue).

To execute this from the grails console needed one extra line to tell the JMS template to use a topic rather than a queue:

def connectionFactory = ctx.getBean("connectionFactory")
def template = new org.springframework.jms.core.JmsTemplate(connectionFactory)
template.setPubSubDomain(true)
template.convertAndSend("test/topic", "Message Posted!")

et voilà
GOT PUBLISHED MESSAGE: Message Posted!

Set the pub sub domain to false and no message is received for SampleTopicService though the previous SampleQueueService works on its destination and visa versa.

Not really the answer to the question Thomas posted here, but it may help with the aspect he mentioned here.

After I sort of set a challenge when thinking about Convention over Configuration, I had to see if it was in fact doable in a framework that exploits the principals.

This was straight from the grails site for the JMS Plugin, but in less than 30 minutes I have an exposed message driven bean receiving a JMS message and that includes downloading the plug-in and Apache ActiveMQ.

As I say, I had to go to download the plugin since, due to what I think is a proxy issue, I couldn’t directly use grails install-plugin jms

Though the following worked fine enough
grails install-plugin C:\Local\downloads\grails-jms-0.3.zip

I needed to copy over three libraries from the ActiveMQ distribution and add a little bit of Spring

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
    <bean id = "connectionFactory" class = "org.apache.activemq.ActiveMQConnectionFactory">
        <property name = "brokerURL" value = "tcp://localhost:61616"/>
    </bean>
</beans>

I then added the service (much like the xfire one) to receive messages (the message driven bean).

class SampleQueueService {
    static expose = ['jms']

    def onMessage(messageObject) {
       println "GOT MESSAGE: $messageObject"
    }

}

Then it was just a matter of running the grails console and entering three lines to send a messge:

def connectionFactory = ctx.getBean("connectionFactory")
def template = new org.springframework.jms.core.JmsTemplate(connectionFactory)
template.convertAndSend("sampleQueue", "Message Posted!")

et voilà
GOT MESSAGE: Message Posted!
I may be easily pleased, but I found that quite satisfying.