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POHow to handle no entity in database for entered parameters?
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copied!<p>I am trying to implement simple login system. I have a JSP with form where user enters username and password, and then servlet that is reading those parameters. You'll understand from servlet code:</p> <pre><code>User user = userDao.findUserWithUsernameAndPassword(username, password); // user found if (user!=null) { session = request.getSession(true); session.setAttribute("user", user); loginMessage = "Welcome"; request.setAttribute("loginMessage", loginMessage); RequestDispatcher dispatcher = request.getRequestDispatcher("login.jsp"); dispatcher.forward(request, response); } else // username and password not matching { loginMessage = "Wrong username or password! Please try again."; request.setAttribute("loginMessage", loginMessage); RequestDispatcher dispatcher = request.getRequestDispatcher("login.jsp"); dispatcher.forward(request, response); } </code></pre> <p>This works if I enter valid username and password, but if not I am getting next exception: </p> <pre><code>javax.persistence.NoResultException: Query "SELECT u FROM User u WHERE u.username like :username AND u.password LIKE :password" selected no result, but expected unique result. </code></pre> <p>What is the proper way of handling this situation? I would like for wrong username and password parameters to display appropriate message (forwarding in 'loginMessage' variable).</p> <p>[added]This is the code in UserDAOBean:</p> <pre><code>@Stateless @Local(UserDAOLocal.class) @TransactionManagement(TransactionManagementType.CONTAINER) @TransactionAttribute(TransactionAttributeType.REQUIRED) public class UserDAOBean extends GenericDAOBean<User, Integer> implements UserDAOLocal{ public User findUserWithUsernameAndPassword(String username, String password) { Query q = em.createNamedQuery("findUserWithUsernameAndPassword"); q.setParameter("username", username); q.setParameter("password", password); User result = (User) q.getSingleResult(); return result; } } </code></pre> <p>And named query in entity User is:</p> <blockquote> <p>@NamedQuery(name = "findUserWithUsernameAndPassword", query = "SELECT u FROM User u WHERE u.username like :username AND u.password LIKE :password")</p> </blockquote>

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