Transaction Management in multiple Entities in one transaction

I am a new user on OpenJPA,
I have a scenario where I need to perform update/insert in multiple entities on one transaction. How to achieve this?

example of EntityManager update method (auto generated by Rational Software Architect8.0.3). [ The same way, I have two more entities. ]
==================
@Action(Action.ACTION_TYPE.UPDATE)
public String updateKna1(Kna1 kna1) throws Exception {
EntityManager em = getEntityManager();
try

{ em.getTransaction().begin(); kna1 = em.merge(kna1); em.getTransaction().commit(); }

catch (Exception ex) {
try {
if (em.getTransaction().isActive())

{ em.getTransaction().rollback(); }

} catch (Exception e)

{ ex.printStackTrace(); throw e; }

throw ex;
} finally

{ ////em.close(); }

return "";
}

==========================
If I keep commit/rollback in each entity then I can not rollback from all previous entities (if last entity insert or update fails).

Can you help me on this?

Thanks in Advance.