Java Servlet切换执行顺序[关闭]

Question

我在使用来自 servlet 的两个开关时遇到了一些问题。我正在尝试从 jsp 上的这些开关加载数据，但它基本上只是在第一个开关上得到，而第二个没有执行。我试过只创建一个开关，但它会给我Cannot forward after response has been committed 等错误。你们知道解决这个问题的正确方法是什么吗？ 谢谢！

这是代码：

public class UserControllerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    private UserDao userDao;
    private ReservationDao reservationDao;
    private DBConnection dbConnection;


    @Override
    public void init() throws ServletException {
        super.init();

        try {
            userDao = new UserDao(dbConnection);
            reservationDao = new ReservationDao(dbConnection);
        }catch(Exception e) {
            throw new ServletException(e);
        }
    }




    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {

        try {
            // read the "command" parameter
            String theCommand = request.getParameter("command");
            String theCommand2 = request.getParameter("command2");
            if(theCommand == null) {
                theCommand = "LIST";
            }

            if(theCommand2 == null) {
                theCommand2 = "LIST";
            }

            switch(theCommand2) {
            case "LIST":
                listReservations(request, response);
                return;

            case "ADD":
                addReservation(request, response);
                return;


            case "LOAD":
                loadReservation(request, response);
                return;


            case "UPDATE":
                updateReservation(request, response);
                return;



            case "DELETE":
                deleteReservation(request, response);
                return;


            default:
                listReservations(request, response);
        }

            //route to the appropriate method
            switch(theCommand) {
                case "LIST":
                    listUsers(request, response);
                    break;

                case "ADD":
                    addUser(request, response);
                    break;


                case "LOAD":
                    loadUser(request, response);
                    break;


                case "UPDATE":
                    updateUser(request, response);
                    break;



                case "DELETE":
                    deleteUser(request, response);
                    break;


                default:
                    listUsers(request, response);
            }

        }catch(Exception e) {
            throw new ServletException(e);
        }

    }

    private void deleteUser(HttpServletRequest request, HttpServletResponse response) 
    throws Exception {
        String theUserId = request.getParameter("userId");

        userDao.deleteUser(theUserId);

        listUsers(request, response);
    }

    private void updateUser(HttpServletRequest request, HttpServletResponse response) 
            throws Exception {

        int id = Integer.parseInt(request.getParameter("userId"));
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String role = request.getParameter("role");
        String nume = request.getParameter("nume");
        String prenume = request.getParameter("prenume");
        String email = request.getParameter("email");
        String adresa = request.getParameter("adresa");
        UserBean theUser = new UserBean(id, username, password, role,nume,prenume,email,adresa);
        userDao.updateUser(theUser);
        listUsers(request, response);
    }

    private void loadUser(HttpServletRequest request, HttpServletResponse response) throws Exception {
        String theUserId = request.getParameter("userId");
        UserBean theUser = userDao.getUser(theUserId);
        request.setAttribute("THE_USER", theUser);
        RequestDispatcher dispatcher = 
                request.getRequestDispatcher("/update-user-form.jsp");
        dispatcher.forward(request, response);
        return;
    }

    private void addUser(HttpServletRequest request, HttpServletResponse response) throws Exception {

        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String role = request.getParameter("role");
        String nume = request.getParameter("nume");
        String prenume = request.getParameter("prenume");
        String email = request.getParameter("email");
        String adresa = request.getParameter("adresa");
        UserBean theUser = new UserBean(username, password, role,nume,prenume,email,adresa);
        userDao.addUser(theUser);
        listUsers(request, response);

    }

    private void listUsers(HttpServletRequest request, HttpServletResponse response) 
    throws Exception {
        List<UserBean> users = userDao.getUsers();
        request.setAttribute("USER_LIST", users);
        RequestDispatcher dispatcher = request.getRequestDispatcher("/list-users.jsp");
        dispatcher.forward(request, response);
        return;
    }


    //Reservations Methods

    private void deleteReservation(HttpServletRequest request, HttpServletResponse response) 
            throws Exception {
                String theReservationId = request.getParameter("reservationId");
                reservationDao.deleteReservation(theReservationId);
                listReservations(request, response);
            }

            private void updateReservation(HttpServletRequest request, HttpServletResponse response) 
                    throws Exception {

                int idReservation = Integer.parseInt(request.getParameter("reservationId"));
                int idUser = Integer.parseInt(request.getParameter("userId"));
                String dataCheckin = request.getParameter("dataCheckin");
                String dataCheckout = request.getParameter("dataCheckout");
                int nrPersoane = Integer.parseInt(request.getParameter("nrPersoane"));
                int nrCamere = Integer.parseInt(request.getParameter("nrCamere"));
                ReservationBean theReservation = new ReservationBean(idReservation, idUser, dataCheckin, dataCheckout,nrPersoane,nrCamere);
                reservationDao.updateReservation(theReservation);
                listReservations(request, response);
            }

            private void loadReservation(HttpServletRequest request, HttpServletResponse response) throws Exception {
                String theReservationId = request.getParameter("reservationId");
                ReservationBean theReservation = reservationDao.getReservation(theReservationId);
                request.setAttribute("THE_RESERVATION", theReservation);
                RequestDispatcher dispatcher = 
                        request.getRequestDispatcher("/update-reservation-form.jsp");
                dispatcher.forward(request, response);
                return;
            }

            private void addReservation(HttpServletRequest request, HttpServletResponse response) throws Exception {

                int userId = Integer.parseInt(request.getParameter("userId"));
                String dataCheckin = request.getParameter("dataCheckin");
                String dataCheckout = request.getParameter("dataCheckout");
                int nrPersoane = Integer.parseInt(request.getParameter("nrPersoane"));
                int nrCamere = Integer.parseInt(request.getParameter("nrCamere"));
                ReservationBean theReservation = new ReservationBean(userId, dataCheckin, dataCheckout,nrPersoane,nrCamere);
                reservationDao.addReservation(theReservation);
                listReservations(request, response);

            }

            private void listReservations(HttpServletRequest request, HttpServletResponse response) 
                throws Exception {
                    List<ReservationBean> reservations = reservationDao.getReservations();
                    request.setAttribute("RESERVATION_LIST", reservations);
                     request.getRequestDispatcher("/list-users.jsp").forward(request, response);
                    return;
                }


    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

}

Answer 1

进入第一个开关，第二个不执行

您的第一个 switch 包含 return 语句。将它们更改为 break 语句。

switch(theCommand2) {
case "LIST":
    listReservations(request, response);
    break; // not return.
case "ADD":
    addReservation(request, response);
    break; // not return..
// ...