UserDAO.java 文件源码

public static User getUser(String username) {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("userData");
    EntityManager em = emf.createEntityManager();
    EntityTransaction tx = em.getTransaction();
    tx.begin();
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<User> q = cb.createQuery(User.class);
    Root<User> c = q.from(User.class);
    q.select(c).where(cb.equal(c.get("username"), username));
    TypedQuery<User> query = em.createQuery(q);
    List<User> users = query.getResultList();
    em.close();
    LOGGER.info("found " + users.size() + " users with username " + username);
    if (users.size() == 1)
        return users.get(0);
    else
        return null;
}