用JSP和Servlet发布问题？

Question

I want to create a small quiz app in jsp which will ask the questions which are stored in the array. It should ask the ask until the last index of array. Here answer is also stored in the array. What I have done so far is:

Main Servlet

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

        try (PrintWriter out = response.getWriter()) {
            session = request.getSession(true);
            Quiz quiz = new Quiz();
            if (session.isNew()) {

                quiz.setTotalCorrectAnswers(0);
                quiz.setCounter(0);
                question = quiz.getNextQuestion(0);
                answer = quiz.getAnswer(0);
            }

            session.setAttribute("quizes", quiz);
            request.setAttribute("quiz", quiz);
            request.setAttribute("currentQuestion", question);
            request.setAttribute("error", false);
            RequestDispatcher view = request.getRequestDispatcher("quiz.jsp");
            view.forward(request, response);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try (PrintWriter out = response.getWriter()) {
            String userAnswer = request.getParameter("txtAnswer");
            Quiz quiz = (Quiz) session.getAttribute("quizes");
            boolean error = false;

            if (userAnswer.equals(quiz.getAnswer(quiz.getCounter()))) {
                totalQuestions++;
                quiz.setTotalCorrectAnswers(totalQuestions);
                quiz.setCounter(quiz.getCounter() + 1);
                session.setAttribute("nextQuestion", quiz.getCounter() + 1);
            } else {
                quiz.setTotalCorrectAnswers(totalQuestions);
                quiz.setCounter(quiz.getCounter());
                error = true;
            }
            session.setAttribute("quizes", quiz);

            if(quiz.getTotalCorrectAnswers()>=5){
                session.invalidate();
                generateQuizOverPage(out);
            }else{
                request.setAttribute("quiz", quiz);
                request.setAttribute("currentQuestion", quiz.getNextQuestion(quiz.getCounter()));
                request.setAttribute("error", error);
                RequestDispatcher view = request.getRequestDispatcher("quiz.jsp");view.forward(request, response);

            }            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

The Quiz model

String[] numberSeries = {
        "3, 1, 4, 1, 5, ",
        "1, 1, 2, 3, 5, ",
        "1, 4, 9, 16, 25, ",
        "2, 3, 5, 7, 11, ",
        "1, 2, 4, 8, 16, "
    };

    String[] answer = {"9", "8", "36", "13", "32"};

    private int counter;
    private boolean isCorrect;
    private int totalCorrectAnswers;

    public Quiz() {
        counter = 0;
        isCorrect = false;
        totalCorrectAnswers = 0;
    }

    public int getCounter() {
        return counter;
    }

    public void setCounter(int counter) {
        this.counter = counter;
    }

    public boolean isIsCorrect() {
        return isCorrect;
    }

    public void setIsCorrect(boolean isCorrect) {
        this.isCorrect = isCorrect;
    }

    public int getTotalCorrectAnswers() {
        return totalCorrectAnswers;
    }

    public void setTotalCorrectAnswers(int totalCorrectAnswers) {
        this.totalCorrectAnswers = totalCorrectAnswers;
    }

    public String getNextQuestion(int index) {
        return numberSeries[index];
    }

    public String getAnswer(int index) {
        return answer[index];
    }

and the quiz.jsp file:

<%@page import="com.app.numberquiz.models.Quiz"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<% 
    Quiz quiz = (Quiz) request.getAttribute("quiz"); 
    String currQuest = (String) request.getAttribute("currentQuestion");
    Boolean error = (Boolean) request.getAttribute("error");
%>

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <form method='post'>
        <h3>Have fun with NumberQuiz!</h3>
        <p>Your current score is: 
        <% out.print(quiz.getTotalCorrectAnswers()); %>  </br></br>
        <p>Guess the next number in the sequence! </p>
        <p>["<% out.print(currQuest); %><span style='color:red'>?</span>"]</p>

        <p>Your answer:<input type='text' name='txtAnswer' value='' /></p>


        <% if (error) {  %>
            <p style='color:red'>Your last answer was not correct! Please try again</p>
        <% } %>
        <p><input type='submit' name='btnNext' value='Next' /></p>

        </form>
    </body>
</html>

In the first run it shows the view correctly but when I reload the page it start to show null in the currQues in the view is it a problem in session if yes then where i have done wrong can anyone please explain it to me thank you!!

Answer 1

When you reload the page doGet method will work, you are setting question if the session is newly created and you put it in request. So when you reload your page session is not newly created and your currentQuestion is not set. You schould add an else case and assign the question or you should put these variables also in your session and retrieve it from the session in your jsp.