acknowledgement mode

[Christophe Verré]

I don't get the point of acknowledgement mode for message driven beans (Auto-acknowledge, Dups-ok-acknowledge). Is this part of the exam objectives ?

[Celinio Fernandes]

I am not sure it is on the exam, has anyone seen a question related to message acknowledgment ?

Anyways, to answer your question:

 
<acknowledgement-mode>Auto-acknowledge</acknowledgement-mode>
Or
<acknowledgement-mode>Dups-ok-acknowledge</acknowledgement-mode>

Auto-acknowledge : tells the container that it should send an acknowledgment to the JMS provider soon after the message is given to an MDB instance to process
Dups-ok-acknowledge : tells the container that it doesn't have to send the acknowledgment immediately

So the bottom line is that auto-acknowledge will not send duplicate messages while dups-ok-acknowledge might send a message that has already been sent.

[vidya sagar]

Is this part of the exam objectives ?

Yes