JMS is one of the oldest Java EE specifications (JMS 1.0 specification is dated 11/1999), however, questions about the difference between message acknowledgement and transacted session still come up. The difference is especially subtle when programmatic client acknowledgement (Session.CLIENT_ACKNOWLEDGE) is used since Message.acknowledge() and Session.recover() are similar to Session.commit() and Session.rollback(). So how are these APIs different?

The bottom line is that there is no difference if you deal only with a single resource (Queue or Topic) within a session. If all you do is consuming messages from a single queue, it does not matter whether you use acknowledgements or transacted sessions (although in my opinion it is more intuitive to use Session.commit/rollback). Session.commit() invokes Message.acknowledge() under the covers and Session.rollback() invokes recover().

However, if you’re dealing with multiple JMS resources withing the same session (or multiple consumers/producers), the transacted session mechanism is what you want to use. For example, you may consume messages from one queue and then put messages on a different queue using the same JMS session. The transacted session will treat all consumed and produced messages as part of a single transaction and will commit or rollback all messages at once. Message acknowledgement on a non-transacted session will “commit” consumed messages independently of the produced ones.

Transacted sessions are limited to JMS resources; container-managed transactions and JTA is required to managed JMS and non-JMS resources (e.g., getting a message from a queue and updating a database).

As a summary, the different mechanisms discussed here differ in terms of the types of resources managed as part of transactions:

* Message acknowledgement: messages consumed from a single destination.
* Transacted session: multiple JMS resources within the same JMS session.
* Container-managed transactions: multiple JMS and non-JMS resources.

For a more in-depth discussion of different transaction mechanisms, refer to this article.

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