Tuesday Feb 11, 2014

JTA 1.2 - It's not your Grandfather's Transactions anymore!

Java Transaction API 1.2 aka JSR 907 (*), which is part of Java EE 7, adds 2 important new features : @Transactional and @TransactionScoped

Prior to JTA 1.2, transactions were delegated to EJBs. By doing that, the developer was shielded from doing low-level JTA/JTS transaction handling as all of this was transparently handeld by the EJB container. With CMT (Container-managed transaction), the default behaviour, the EJB container intercept calls so that it can interpose the required transaction plumbings. So this was, on one hand, handy because transactions were basically managed transparently but it also required, on the other hand, to use EJBs.

The new @Transactional annotation solve this by basically bringing the semantics of those EJB transaction attributes in managed beans without any dependencies on the EJB container. So the @Transactional annotation provides the ability to declaratively control transaction boundaries on managed beans. Under the hood, this capability is provided by a CDI interceptor that handle the necessary transaction plumbings (suspend, resume, commit, ...). In a nutshell, @Transactional bring the ease of CMT transactions to various Java EE Components (Servlet, JAX-RS, etc.) without requiring to use EJBs. 

The new @TransactionScoped annotation provides the ability to specify a standard CDI scope to define bean instances whose lifecycle is scoped to the currently active JTA transaction. This simple code driven post explain and demonstrate such a behaviour in action.

(*) For the curious who might wonder why some JSRs start in the 9xx range, there's a simple explanation for that. Those specifications are referred, in JCP parlance, as "Grandfathered JSRs" because those specifications have originally been developed outside of the JCP.