Login authentication - null pointer exception

Question

I'm trying to validate user credentials using the following code, but I'm getting a null pointer exception every time the method is called:

public class LoginValidator {

    private static EntityManagerFactory emf;

    public static boolean validateUser(String email, String pswd){
        boolean status =  false;
        try{          
            EntityManager em;
            em =  emf.createEntityManager();
            Query q = em.createQuery("select c from Customer c where c.Email=:email and c.Password=:password")
                .setParameter("email", email)
                .setParameter("password", pswd);

            if (q.getResultList() != null)
                status = true;

            }catch(Exception e){System.out.println(e);}
            return status;
    }
}

Can anyone see why this is happening?

Also, is this a good way to perform authentication? I'm not so sure about my use of Query

Answer 1

您尚未实例化/注入EntityManagerFactory emf。

Answer 2

emf为null，您必须初始化它：

private static EntityManagerFactory emf = Persistence.createEntityManagerFactory("persistanceUnitName");

Answer 3

If it is a Java EE application, as you indicate in the tags, use injection for the EntityManager :

@PersistenceContext
EntityManager em;

Do not use the EMF to instantiate the EM, it creates unnecessary overhead.

If it is more than a throw-away excercise, please consider hashing and salting the password, like this:

query.setParameter("password", computeSaltedHash(pswd));