The setRollbackOnly mehtod on the EJBContext can only be used in methods that have a transaction attribute type of REQUIRE, REQUIRED_NEW or MANDATORY. If a transactions hasn't been started, as in the case of SUPPORTED or NEVER, a java.lang.IllegalStateException will be thrown.
What about this case ?
A method is annotated with a transaction attribute type of SUPPORT. And this method will join an existing transaction. Can we roll back changes in this method ? I assume we cannot roll back changes in such a method, based on this quote. Then, is it possible to roll back any changes?
Only enterprise beans that will execute correctly in both modes should use the SUPPORTS transaction attribute.
You can't guarantee that the method will be called with a transaction present so you wouldn't know when to do the rollback and when not to. If a transaction exists it will probably work because the specs only say the exception is thrown if "the instance is not allowed to use this method (i.e. the instance is of a bean with bean-managed transactions)." but it will be very bad practice to use transaction semantics in a method marked as SUPPORTS.
Whether it will throw an exception or not could be implementation specific. The API specs don't explicitly say what will happen. The code is a contradiction. It declares that the method doesn't care about the presence of a transaction and yet it goes on to try and use it.