I have an existing application with stateless session beans using CMT. Methods that don't require a transaction -- typically ones that are only reading from the database -- are marked as "Supports". Others that do updates to multiple tables that must operate atomically are marked as "Required".

I am attempting to convert our current persistence mechanism to Hibernate. I'm using the CMTTransactionFactory in JBoss along with SessionFactory.getCurrentSession as described here:

http://blog.hibernate.org/cgi-bin/blosxom.cgi/2005/04/12

I'm having a problem with the "Supports" methods. If they are not part of a larger transaction, then Hibernate throws a NullPointerException in getCurrentSession (the code appears to expect a transaction to always be available). If I label them all as "Required", then everything works.

What is the preferred way to handle this scenario? Is there a way to use a CMT method marked as "Supports" with Hibernate? Or is it safe/efficient to simply mark all the methods as "Required", even though there are times when the methods don't really need a transaction?

I am wondering about this same scenario. I have an existing app that uses Stateless Session EJBs with CMT. I am researching using Hibernate. Currently, methods that select and do not do update are marked with <trans-attribute>Supports</trans-attribute>. Methods that have several updates that must act as an atomic unit are marked with <trans-attribute>Required</trans-attribute>
I get the NullPointerException when I use Hibernate in the context of a 'Supports' method.
I've done some limited load testing of the app in its current condition 'not using Hibernate'. I get equivalent results in terms of response times when I change all the read-only 'Supports' methods to 'Required'. This makes me feel somewhat ok with changing all trans-attributes to 'Required'.
The application is a very large one that must support heavy user load and perform well. A lot of the EJB methods call each other. I'm a little concerned that if I move to Hibernate and cause all methods that interact with the DB to use container transaction management, I will increase duration of transactions and potentially cause unnecessary wait time and contention.
It would be interesting to know if anyone else has insight into consequences of causing all methods to require a transaction for the duration of the method when using CMT/Hibernate.