How to implement Hibernate DAO with generics

I've found a few tutorials on how to build a Hibernate DAO with generics, but they all use EntityManager instead of a SessionFactory. My question, is how to build a DAO with generics using SessionFactory. I have the below so far:

Interface:

public interface GenericDao<T> {

    public void save(T obj);
    public void update(T obj);
    public void delete(T obj);
    public T findById(long id);
}

Class:

@Repository
public class GenericDaoImpl<T> implements GenericDao<T> {

    @Autowired
    private SessionFactory sessionFactory;

    public void save(T obj) {
        Session session = sessionFactory.openSession();
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            session.save(obj);
            tx.commit();
        } catch (HibernateException e) {
            if(tx != null)
                tx.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }

    }

    public void update(T obj) {
        Session session = sessionFactory.openSession();
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            session.update(obj);
            tx.commit();
        } catch (HibernateException e) {
            if(tx != null)
                tx.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }

    }

    public void delete(T obj) {
        Session session = sessionFactory.openSession();
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            session.delete(obj);
            tx.commit();
        } catch (HibernateException e) {
            if(tx != null)
                tx.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }

    }

    public T findById(long id) {
        // ??
        return null;
    }

I'm unsure how to go about findById using generics. I believe the other methods are right, but correct me if I'm wrong.

SIDE QUESTION: Is using EntityManager more beneficial than using SessionFactory? I saw a few posts on the subject, but would like a few more opinions.