java - javax.persistence.NoResultException: getSingleResult() did not retrieve any entities

Question

i have created a namedquery with ejb to check if the username is used. When the singleResult is null, then i get the following Exception :

javax.persistence.NoResultException: getSingleResult() did not retrieve any entities

But this exception is the result that i want when the username is free.

Here is the code:

 public User getUserByUsername(String username) throws DAOException{
    try{
        Query q = em.createNamedQuery(User.getUserByUsername);
        q.setParameter("username", username);
        return (User) q.getSingleResult();
    }catch(Exception e){
        throwException(username, e);
        return null;
    }
}

Does anybody know what the problem is. :(

I would like to return null and don`t get an Exception.

Thank you very much

Answer 1

You seem to rethrow the exception in your catch block with the statement throwException(username, e);. If you expect to get the user or null without any exception this should look like the following:

public User getUserByUsernameOrNull(String username) {
    try{
        Query q = em.createNamedQuery(User.getUserByUsername);
        q.setParameter("username", username);
        return (User) q.getSingleResult();
    } catch(NoResultException e) {
        return null;
    }
}