posted 16 years ago
I am not sure it is on the exam, has anyone seen a question related to message acknowledgment ?
Anyways, to answer your question:
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.