UserDAO.java 文件源码

/**
 * retrieves the list of user emails registered.
 * 
 * @return users the list of user emails
 * 
 */
public static List<String> listUsers() {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("userData");
    EntityManager em = emf.createEntityManager();
    Query query = em.createQuery("SELECT username FROM User");
    @SuppressWarnings("unchecked")
    List<String> users = query.getResultList();
    em.close();
    return users;
}