Want to handle declarative transactions at the service layer

//DAO
@Transactional
public class UserDAO implements UserDAO Interface {

    @ Inject
    EntityManagerem;

    public User find(intid){
        return em.find(User.class,id);
    }

    @ Override
    public void update (User user) {
        // TODO Auto-generated method stub
        em.merge(user);
        em.flush();
    }

    // Transaction processing is successful (rollback) here
    public void transaction (User buyer, Item item) {
        User seller=find(item.getSellerId());
        int price = item.getPrice();
        buyer.setBalance(buyer.getBalance()-price);
        update(buyer);
        if(true){
            through new RuntimeException();
        }
        seller.setBalance(seller.getBalance()+price);
        update(seller);
    }

}

// Service Layer (Business Logic)
@Transactional
public class UserLogic implements UserLogicInterface {

    UserDAOInterface dao=Guice.createInjector (new JpaPersistDaoModule())
            .getInstance(UserDAO.class);

    publicUser signIn(String email, String password) {
        return dao.find(email, password);
    }

    // This will not run (rollback) successfully
    public void transaction (User buyer, Item item) {
        User seller=dao.find(item.getSellerId());
        int price = item.getPrice();
        buyer.setBalance(buyer.getBalance()-price);
        dao.update(buyer);
        if(true){
            through new RuntimeException();
        }
        seller.setBalance(seller.getBalance()+price);
        dao.update(seller);
    }

}