Hi all,

Suppose we are implementing the code for "register a new user to Spring forum". And you need to guarantee that username is unique...

(There is a service layer, a dao layer, and a view layer. Using declarative transaction management.)

Here is what i thought:

hmm, i can put a constraint check in database, let Spring throw DataIntegrityViolationException and catch it in the service layer and
wrap it within a more specific and meaningful exception and throw the new exception.

Here is the service layer code:
Code:
    @Transactional
    public void save(User User) {
        try {
            dao.save(user);
        } catch (DataIntegrityViolationException ex) {
            throw new BusinessException("Duplicate username.");
        }
    }
You might guess what actually happens in this situation; i can't catch the exception, because dao.save(user) would not really save to the database
(hence the constraint viloation does not manifest) until transaction commits (when the save method exits).

Any suggestion? What do you think i should do?