Using and controlling Spring transactions within Struts 2 actions

Generally, controllers/actions/backing beans/etc don't handle transactions. Actions are the web-part of your back-end code - they should only be concerned with gathering request data, and sending response data. The logic itself (including database access) should be done in another layer. E.g. a service layer. So you create another bean, inject it in the action, and make it do the work - userService.register(user). Then configuring transactions on a service layer should be trivial since it is both in the spring documentation and in countless examples:

<tx:annotation-driven /> and @Transactional (btw, make sure you have the <tx:..> now, it might be causing the issue. Even if it works, this does not invalidate my suggestion about the service layer)

I don't like answering my own question, but since I solved this ages ago... I thought I should share the knowledge (or lack of... in this case).

The book I was using to learn about Struts 2 and Spring-JPA-Hibernate, adds the @Transactional annotation right before the declaration of the service class. This is terribly wrong, for all methods (including those that only retrieve stuff from the database) are inside a committable transaction. Long story short everything got committed event if exceptions occurred.

The solution, as Bozho so wisely pointed out, was to look at examples. That is, set your transtactional methods carefully, in my case I set up transactions for the methods that had to write back to the database and everything started to work just fine.

Thanks to Steven and Quaternion too for taking the time to answer my question.