PersistenceManager pm = pmf.getPersistenceManager();
Transaction tx = pm.currentTransaction();
try
{
    tx.begin();

    tx.setSynchronization(new javax.transaction.Synchronization()
    {
        public void beforeCompletion()
        {
             // before commit or rollback
        }

        public void afterCompletion(int status)
        {
            if (status == javax.transaction.Status.STATUS_ROLLEDBACK)
            {
                // rollback
            }
            else if (status == javax.transaction.Status.STATUS_COMMITTED)
            {
                // commit
            }
        }
    });
    
    tx.commit();
}
finally
{
    if (tx.isActive())
    {
        tx.rollback();
    }
}
pm.close();