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The scope and lifetime of the Session attribute in Servlet in my web application confuse me when using more than two tabs of the same browser

I was doing a simple web project (you can see the code below). As far as I know, session attributes are associated with a single session. When I open two tabs of the same browser and launch the URL type, only one session identifier is created, but two different objects of the same session attribute are executed (i.e. I do not want to run two quizzes at the same time. When I changed the question to one of tabs, this does not affect the session attributes of another tab). Can you explain to me why this happened? How can I change my code to make shared session variables so that when I change one of the session attributes on one of the tabs, I want the other session variables of the tab to be affected?

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package com.quizServlet;

import QuizApp.Quiz;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 *
 * @author Mati
 */
@WebServlet(name = "QuizServlet", urlPatterns = {"/Quiz"})
public class QuizServlet extends HttpServlet {

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
        } catch (Exception ex) {
            out.write("<font style='color:red'><b>" + ex.getMessage() + "</b></font>");
        } finally {
            out.close();
        }
    }

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

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            if (request.getSession().getAttribute("QuizzObject") == null) {
                Quiz quiz = new Quiz();
                quiz.addQuestion(new int[]{1, 2, 3, 4});
                quiz.addQuestion(new int[]{1, 1, 2, 3, 5, 8});
                quiz.addQuestion(new int[]{0, 5, 10, 15, 20, 25});
                request.getSession().setAttribute("QuizzObject", quiz);
            }
            if (request.getSession().getAttribute("questionsLeft") == null) {
                request.getSession().setAttribute("questionsLeft", true);
            }
                        Quiz qq = (Quiz) request.getSession().getAttribute("QuizzObject");
                        qq.reset();

            StringBuilder SB = new StringBuilder();

            SB.append("<form name='myform' method='post'>");
            SB.append("<h3>Have fun with NumberQuiz!</h3>");
            SB.append("<p><input type='submit' name='btnNext' value='Start quiz' /></p>");
            SB.append("</form>");
            out.print(SB.toString());

        } catch (Exception ex) {
            out.write("<font style='color:red'><b>" + ex.getMessage() + "</b></font>");
        } finally {
            out.close();
        }
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        PrintWriter out = response.getWriter();

        try {

            StringBuilder SB = new StringBuilder();
            String msg="";
            SB.append("<html><head></head><body>");
            Quiz qq = (Quiz) request.getSession().getAttribute("QuizzObject");
            SB.append(request.getSession().getId());
            boolean questionsLeft = (Boolean) request.getSession().getAttribute("questionsLeft");
            if (questionsLeft) {
                qq.addAttempts();
                if (request.getParameter("txtAnswer") != null) {
                    if (qq.isCorrect(Integer.parseInt(request.getParameter("txtAnswer")))) {
                        qq.scoreAnswer();
                    } else {
                        msg="<p><font style='color:red'>Wrong Answer .. Try Again</font></p>";
                    }
                }
                if (qq.getCurrentQuestion() == null) {
                    request.getSession().setAttribute("questionsLeft", false);
                    SB.append("Congratulations, you have completed the quiz!");
                    SB.append("<br>Your final score is:" + qq.getScore());
                    SB.append("<br>Total attempts:" + qq.getAttempt());
                    qq.reset();
                    request.getSession().setAttribute("questionsLeft",null);
                } else {
                    SB.append("<form name='myform' method='post'>");
                    //SB.append("<h3>Have fun with NumberQuiz!</h3>");
                    SB.append("<p>Your current score is " + qq.getScore() + ".</p>");
                    SB.append("<p>Guess the next number in the sequence!</p>");
                    SB.append("<p>" + qq.getCurrentQuestion().toString().replaceAll("\\?", "<font style='color:red'><b>?</b></font>") + "</p>");
                    SB.append("<p>Your answer:<input type='text' id='txtAnswer' name='txtAnswer' value='' /></p>");
                    SB.append("<p><input type='submit' name='btnNext' value='Next' onclick='return validate()' />");
                    SB.append("<input type='Reset' name='btnStart' value='Restart!' onclick=\"document.location.href='/QuizzWeb/Quiz';return false;\" /></p>");
                    SB.append(msg);
                    SB.append("</form>");
                    SB.append("<script type='text/javascript'>function validate(){if(document.getElementById('txtAnswer').value==''){alert('You should write an answer');return false;}return true;}</script>");
                }
                SB.append("</body></html>");
                out.print(SB.toString());
            }

        } catch (Exception ex) {
            out.print("<font style='color:red'><b>" + ex.getMessage() + "</b></font>");
        } finally {
            out.close();
        }

    }

    @Override
    public String getServletInfo() {
        return "Short description";
    }
}
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2 answers

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package test.servlets;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.atomic.AtomicInteger;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Counting servlet counts the number of requests to it.
 * @author Charlie Huggard-Lee
 */
@SuppressWarnings("nls")
public class CountingServlet extends HttpServlet {

/**
 * The serialVersionUID.
 */
private static final long serialVersionUID = 4279853716717632192L;

/**
 * {@inheritDoc}
 */
@Override
protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws IOException {
    final HttpSession session = req.getSession();
    AtomicInteger counter = (AtomicInteger) session.getAttribute("Count");
    if (counter == null) {
        counter = new AtomicInteger();
        session.setAttribute("Count", counter);
    }

    final boolean checkOnly = Boolean.parseBoolean(req.getParameter("checkOnly"));

    final int thisCount;
    if (checkOnly) {
        thisCount = counter.get();
    } else {
        thisCount = counter.getAndIncrement() + 1;
    }

    resp.setStatus(200);
    resp.setHeader("Content-Type", "text/plain"); //$NON-NLS-1$ //$NON-NLS-2$
    resp.setCharacterEncoding("UTF-8"); //$NON-NLS-1$
    final PrintWriter writer = resp.getWriter();

    if (session.isNew()) {
        writer.append("Hey new user!\n");
    } else {
        writer.append("Welcome Back!\n");
    }
    writer.append("Session ID: ");
    writer.append(session.getId());
    writer.append("\n");
    if (checkOnly) {
        writer.append("(checking) ");
    }
    writer.append("Count: ");
    writer.append(Integer.toString(thisCount));
    }
}
+7

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