ActiveMQ onMessage never works with createDurableSubscriber - kotlin

Question

I have been trying to find out why onMessage is not getting invoked in the below code. I am able to publish a set of objects to a Topic name "SampleTopic" successfully, but I am not able to consume from it. Nothing has worked for me. Please suggest.
val logger = KotlinLogging.logger {}
logger.info { "This is info log : Inside subscriber" }
val connFactory = ActiveMQConnectionFactory()
val conn = connFactory.createConnection()!!
conn.setClientID("SampleClient")
val sess = conn.createSession(false, Session.AUTO_ACKNOWLEDGE)
val dest = sess.createTopic("SampleTopic")
val cons : TopicSubscriber = sess.createDurableSubscriber(dest, "SampleSubscription")
logger.info { "This is info log : Inside subscriber $cons" }
conn.start()
Thread.sleep(10000)
logger.info { "This is info log : Inside subscriber $cons" }
cons.setMessageListener {
MessageListener() {
fun onMessage(message: Message?) {
try {
logger.info { "This is info log : Inside subscriber1 : $message" }
} catch (e: NumberFormatException) {
e.printStackTrace()
} catch (e: JMSException) {
e.printStackTrace()
}
}
}
}
logger.info { "This is info log : Inside subscriber90 $cons" }
conn.close()
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Answer 1

As soon as you set the MessageListener you invoke close() on the connection. Closing the connection will close all related sessions along with all the producers and consumers created from those sessions. Therefore you won't be able to receive any messages. Once you set the MessageListener you'll need to keep the connection open so it can receive messages.
Keep in mind that the purpose of the MessageListener is to receive messages asynchronously. You need to keep the connection open during this time.
The simplest way to keep the connection open is just to insert a Thread.sleep() after you set the MessageListener. However, this effectively makes your client synchronous.
Alternatively, you can receive messages synchronously. This bit of code will consume all the messages it can until it doesn't receive a message for 10 seconds:
val logger = KotlinLogging.logger {}
logger.info { "This is info log : Inside subscriber" }
val connFactory = ActiveMQConnectionFactory()
val conn = connFactory.createConnection()!!
conn.setClientID("SampleClient")
val sess = conn.createSession(false, Session.AUTO_ACKNOWLEDGE)
val dest = sess.createTopic("SampleTopic")
val cons : TopicSubscriber = sess.createDurableSubscriber(dest, "SampleSubscription")
logger.info { "This is info log : Inside subscriber $cons" }
conn.start()
Thread.sleep(10000)
logger.info { "This is info log : Inside subscriber $cons" }
do {
val message = cons.receive(10000)
logger.info { "This is info log : $message" }
} while (message != null)
logger.info { "This is info log : Inside subscriber90 $cons" }
conn.close()