java - 向同一页面和同一 servlet 发送请求参数

Question

所以，我试图从下拉列表中获取值并将它们添加到 ArrayList 以便稍后我可以显示它，但我不知道该怎么做？

基本上，当用户按下下一步(发送)按钮时，Servlet 应该获取值参数，并将其存储到数组列表中以供以后使用，并且应该将他们引导回表单页面，以便他们可以进行更多选择或通过按完成(列表)按钮查看他们选择了哪些选项

Servlet(水果servlet)

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        response.setContentType("text/html;charset=UTF-8");

            String wasSent = request.getParameter("send");
            String Submitted = request.getParameter("list");
            ArrayList<Double> fruitsList = new ArrayList<Double>();


            if (wasSent != null) {
                String fruits = request.getParameter("Values");
                fruitsList.add(fruits);
                request.setAttribute("List", fruitsList);
                RequestDispatcher rs = request.getRequestDispatcher("form.html");
                rs.forward(request, response);

            } else if (Submitted != null) {

                //get the list and display all the values
            }

        }

Answer 1

在您的 servlet 中您可以使用 session在数组中设置您的值，以便该值将被保存，直到您将其从 session 中删除。您的代码将如下所示:

 protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        response.setContentType("text/html;charset=UTF-8");

           String fruits = request.getParameter("Values");
            ArrayList<String> fruitsList1 = new ArrayList<String>();
           //get values which are in session
            ArrayList<String> fruitsList = (ArrayList<String>)request.getSession().getAttribute("List");

              //if attribute value is not null 
            if (fruitsList != null) {
               //add new values
                fruitsList.add(fruits);
                request.getSession().setAttribute("List", fruitsList);
                RequestDispatcher rs = request.getRequestDispatcher("form.html");
                rs.forward(request, response);

            } else if (fruitsList== null) {
               //adding value selected in array list
                fruitsList1.add(fruits);
                 //setting values
                request.getSession().setAttribute("List", fruitsList1);
                RequestDispatcher rs = request.getRequestDispatcher("form.html");
                rs.forward(request, response);
            } else{

             //remove values 
         }

        }