Who manages a JMS session on the consumer side - jms

If I have a JMS queue and I wish to put a message on the queue from a publishing client, I need to first open a session, get the queue from its jndi name and then send the message to the queue.
But on the consumer side, how come I do not manually need to open a session and receive the message. Does the container always keep one open session per MDB (considering one MDB listening on one queue)

If you're using MDB's, which are container-managed objects, the connection, session, queue/topic, and actual consumer are all managed by the container.
You just write the code for onMessage(Message m), that's it.

Related

What does Spring JMS ActiveMQ use to determine when a broker should switch Exclusive Consumers?

An exclusive consumer in Activemq is one that is sent every message from a broker until the consumer dies or goes away, at which time the broker switches consumer.
What is it that defines when the switchover takes place? How do you configure this in Spring JMS/ActiveMQ?
It's not Spring JMS doing the checking; it's the JMS provider, ActiveMQ.
JMS is an API specification; an empty framework, essentially. ActiveMQ provides the implementation backing for managing connections, message brokering, load-balancing, fail-over, etc.
The ActiveMQ broker handles switching-over consumers based on queue properties (you don't need to do anything special in your code):
queue = new ActiveMQQueue("TEST.QUEUE?consumer.exclusive=true");
The switch-over takes place when either the consumer disconnects gracefully or the broker determines that the consumer has disappeared (via the wireFormat.maxInactivityDuration elapsing without any messages or keep-alives being received). You don't have to configure anything if you're happy with the default value of wireFormat.maxInactivityDuration (30 seconds), but you can tweak that if you want to change how long it takes before the broker gives up on a client.

single jms consumer for multiple jms servers

I am using a distributed jms queue and weblogic is my app server. There are three jms servers deployed in my clustered enviroment. The producers just send the message using name of queue jndi lookup 'udq' for example. Now I have associated a consumer for each jms server and I was able to consume the message, no problem so far.
Here is question, can I have a single consumer to consume the messages from the 3 jms servers. The weblogic allows jndi naming for destination lookup with following syntax #
qsession1 = qcon1.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);
qsession2 = qcon2.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);
qsession3 = qcon3.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);
queue1 = (Queue)ctx.lookup("JMSServer-1#UDQ");
queue2 = (Queue)ctx.lookup("JMSServer-2#UDQ");
queue3 = (Queue)ctx.lookup("JMSServer-3#UDQ");
qreceiver1 = qsession1.createReceiver(queue1);
qreceiver2 = qsession2.createReceiver(queue2);
qreceiver3 = qsession3.createReceiver(queue3);
qreceiver1.setMessageListener(this);
qreceiver2.setMessageListener(this);
qreceiver3.setMessageListener(this);
qcon1.start();
qcon2.start();
qcon3.start();
I have only one OnMessage implemented for the above consumer. This does not work. Any suggestions please..
No, you can't have a consumer receiving messages from more than one JMS server. A consumer can receive messages from only one JMS server. You need to create multiple consumers to receive messages from multiple JMS servers.
you can use "Queue Forwarding" function.
From online documentation of wls 10.3:
"Queue members can forward messages to other queue members by configuring the Forward Delay attribute in the Administration Console, which is disabled by default. This attribute defines the amount of time, in seconds, that a distributed queue member with messages, but which has no consumers, will wait before forwarding its messages to other queue members that do have consumers."
here a link: http://docs.oracle.com/cd/E13222_01/wls/docs103/jms/dds.html#wp1260816
You can configure this feature from administration of each single queue.

How do I hold a jms message in queue until it is saved?

I just started using Weblogic JMS. I was able to send messages to the queue and pull them off with a messagebean. Now I want to save the message to a database.
So my question is, how do I tell JMS not to delete the message from the queue until I have successfully written the message to the database?
Thanks
I was able to send messages to the queue and pull them off with a
messagebean.
I suppose you are talking about message-driven bean (MDB)?
So my question is, how do I tell JMS not to delete the message from
the queue until I have successfully written the message to the
database?
MDBs are part of implicit container-managed transaction and the message will not be removed as long as your transaction hasn't commited (that is, as long as your onMessage method hasn't reached its end).
In case of rollback (i.e. you throw an exception or call context.setRollbackOnly() on the MessageDrivenContext), message will be redelivered. You can avoid this behaviour by making transaction bean-managed or using #TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED), but in your situation that should not be the case. Stick with default configuration and everything should work as you wish.

ActiveMQ Session AUTO_ACKNOWLEDGE property impact

Can anyone please explain me what is the impact of Session.AUTO_ACKNOWLEDGE for ActiveMQ JMS configurations
session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
I believe by default ActiveMQ is set to auto acknowledge messages. This just means that when a message arrives it will automatically acknowledge that the message arrived. It is the same thing as calling .acknowledge() from the JMS object.
One reason to turn auto-acknowledge off is if you built a server and lets say you are processing each JMS Message and are doing some sort of DB transaction. If the transaction fails you would want the JMS message to be re-sent so you can fix your error and process it again. So in this sense you would only acknowledge the JMS object only after processing.

JBoss doesn't process JMS messages

Although JBoss seem to receive the JMS messages (I can list them through jmx-console) it doesn't process them. They stayed queued forever. What might be the reason for that?
Do you have a message consumer running to process the queue?
This could be something like a message driven bean, or another JMS client connecting to the queue.

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