HIbernate and active transaction

public User getUserByLogin(String login) throws FunctionnelException {
        
    try {
       session = SessionFactory.getCurrentSession();
       transaction = session.beginTransaction();
       final User user = (User) session.createCriteria(User.class).add(Expression.eq("username", username)).uniqueResult();
         transaction.commit();
         return user;
        }
.....