javaservlet空属性

nkoocmlb  于 2021-06-30  发布在  Java
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这个问题在这里已经有了答案：

如何通过单击jsp页面中的超链接或按钮将当前项传递给java方法(1个答案）
20天前关门了。
我的代码有问题。我正在做一个经销商网站。我的属性得到一个空值。我的程序在jsp上通过arraylist的foreach循环运行，我在每辆车上都有购买它们的按钮。当用户选择购买该商品时，它将获取他们选择的汽车并将其转发到购买页面。但由于一些奇怪的原因，当我进入购买页面时，车的值是空的。任何帮助都将不胜感激。
servlet:

  1. package com.servlets;
  3. import java.io.IOException;
  5. import javax.servlet.RequestDispatcher;
  6. import javax.servlet.ServletException;
  7. import javax.servlet.annotation.WebServlet;
  8. import javax.servlet.http.HttpServlet;
  9. import javax.servlet.http.HttpServletRequest;
  10. import javax.servlet.http.HttpServletResponse;
  11. import javax.servlet.http.HttpSession;
  13. import com.dealership.Car;
  14. import com.dealership.Inventory;
  16. /**
  17.  * Servlet implementation class PurchaseServlet
  18.  */
  19. @WebServlet("/PurchaseServlet")
  20. public class PurchaseServlet extends HttpServlet {
  21.     private static final long serialVersionUID = 1L;
  23.     /**
  24.      * @see HttpServlet#HttpServlet()
  25.      */
  26.     public PurchaseServlet() {
  27.         super();
  28.         // TODO Auto-generated constructor stub
  29.     }
  31.     /**
  32.      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
  33.      */
  34.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  35.         // TODO Auto-generated method stub
  37.     }
  39.     /**
  40.      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  41.      */
  42.     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  43.         // TODO Auto-generated method stub
  45.         HttpSession session = request.getSession(true);
  47.         Car purchaseCar = (Car)session.getAttribute("purchaseCar");
  48.         Inventory inventory = new Inventory();
  49.               if(purchaseCar == null) {
  50.                     purchaseCar = new Car(); 
  52.               }
  53.           if (request.getParameter("purchase") != null) {             
  54.               inventory.test(purchaseCar);
  55.           }
  56.           session.setAttribute("purchaseCar", purchaseCar);
  58.         RequestDispatcher rs = request.getRequestDispatcher("purchase.jsp");
  59.         rs.forward(request, response);
  61.     }
  63. }

jsp地址：

  1. <%@ page language="java" contentType="text/html; charset=UTF-8"
  2.     pageEncoding="UTF-8"%>
  4. <jsp:include page="/HomepageServlet" />
  6. <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
  8. <!doctype html>
  9. <html lang="en">
  10. <head>
  11. <!-- Required meta tags -->
  12. <meta charset="utf-8">
  13. <meta name="viewport"
  14.     content="width=device-width, initial-scale=1, shrink-to-fit=no">
  16. <!-- Bootstrap CSS -->
  17. <link rel="stylesheet"
  18.     href="https://cdn.jsdelivr.net/npm/bootstrap@4.5.3/dist/css/bootstrap.min.css"
  19.     integrity="sha384-TX8t27EcRE3e/ihU7zmQxVncDAy5uIKz4rEkgIXeMed4M0jlfIDPvg6uqKI2xXr2"
  20.     crossorigin="anonymous">
  22. <!-- Local CSS -->
  23. <link rel="stylesheet" href="styles.css" />
  25. <!-- Link to font -->
  26. <link rel="preconnect" href="https://fonts.gstatic.com">
  27. <link
  28.     href="https://fonts.googleapis.com/css2?family=Cinzel:wght@600&display=swap"
  29.     rel="stylesheet">
  31. <title> Tropical Auto</title>
  32. </head>
  33. <body>
  34.     <div>
  35.         <nav class="navbar navbar-expand-lg navbar-light bg-light">
  36.             <a class="navbar-brand" href="#">Nick's Tropical Autocenter</a> <a
  37.                 class="navbar-brand" href="#"> <img src="mango.svg" width="30"
  38.                 height="30" alt="" loading="lazy">
  39.             </a>
  40.             <button class="navbar-toggler" type="button" data-toggle="collapse"
  41.                 data-target="#navbarNav" aria-controls="navbarNav"
  42.                 aria-expanded="false" aria-label="Toggle navigation">
  43.                 <span class="navbar-toggler-icon"></span>
  44.             </button>
  45.             <div class="collapse navbar-collapse" id="navbarNav">
  47.                 <ul class="navbar-nav">
  48.                     <li class="nav-item active"><a class="nav-link"
  49.                         href="index.jsp"> INVENTORY <span class="sr-only">(current)</span></a>
  50.                     </li>
  51.                     <li class="nav-item"><a class="nav-link" href="usedcars.jsp">USED
  52.                             INVENTORY</a></li>
  53.                     <li class="nav-item"><a class="nav-link" href="specials.jsp">SPECIALS</a>
  54.                     </li>
  55.                     <li class="nav-item"><a class="nav-link" href="#">ABOUT US</a>
  56.                     </li>
  57.                 </ul>
  58.                 <form class="d-flex" action="SearchCarsServlet" method="post">
  59.                     <input class="form-control me-2" type="search" name="searchInput"
  60.                         placeholder="Search" aria-label="Search">
  61.                     <button class="btn btn-outline-success" type="submit">Search</button>
  62.                 </form>
  63.             </div>
  64.         </nav>
  65.     </div>
  67.     <div class=album py-5bg-light">
  69.         <div class="container">
  70.             <div class="row row-cols-1 row-cols-sm-2 row-cols-md-3 g-3">
  72.                 <c:forEach var="car" items="${inventory.carList}">
  74.                     <c:if
  75.                         test="${car.used == false && car.residence < 120 && car.purchased == false}">
  76.                         <div class="col">
  77.                             <div class="card" style="width: 18rem;">
  79.                                 <img src=${car.image } class="card-img-top" alt="...">
  80.                                 <div class="card-body">
  81.                                     <p><span class="mandatory">${car.make}${car.model}</span></p>
  82.                                     <p class="card-text">${car.description}
  83.                                 </div>
  85.                                 <div class="d-flex justify-content-center align-items-center">
  86.                                     <form action="PurchaseServlet" method="POST">
  87.                                     <c:set var="purchaseCar" value="${car}" scope="application" />
  88.                                     <button type="submit" name="purchase" class="btn btn-success">Purchase</button>
  89.                                     </form> 
  90.                                     <div class="dropdown">
  91.                                         <a class="btn btn-secondary dropdown-toggle" href="#"
  92.                                             role="button" id="dropdownMenuLink" data-toggle="dropdown"
  93.                                             aria-haspopup="true" aria-expanded="false"> Details </a>
  94.                                         <div class="dropdown-menu details-button"
  95.                                             aria-labelledby="dropdownMenuLink">
  96.                                             <a class="dropdown-item" href="#">Make: ${car.make}</a> <a
  97.                                                 class="dropdown-item" href="#">Model: ${car.model}</a> <a
  98.                                                 class="dropdown-item" href="#">Year: ${car.year}</a> <a
  99.                                                 class="dropdown-item" href="#">Mileage: ${car.mileage}</a> <a
  100.                                                 class="dropdown-item" href="#">Price: $${car.price}</a>                     
  101.                                         </div>
  102.                                     </div>
  104.                                 </div>
  106.                             </div>
  108.                         </div>
  110.                     </c:if>
  112.                 </c:forEach>
  114.             </div>
  116.         </div>
  118.     </div>
  120.     <!-- Optional JavaScript; choose one of the two! -->
  122.     <!-- Option 1: jQuery and Bootstrap Bundle (includes Popper) -->
  123.     <script src="https://code.jquery.com/jquery-3.5.1.slim.min.js"
  124.         integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj"
  125.         crossorigin="anonymous"></script>
  126.     <script
  127.         src="https://cdn.jsdelivr.net/npm/bootstrap@4.5.3/dist/js/bootstrap.bundle.min.js"
  128.         integrity="sha384-ho+j7jyWK8fNQe+A12Hb8AhRq26LrZ/JpcUGGOn+Y7RsweNrtN/tE3MoK7ZeZDyx"
  129.         crossorigin="anonymous"></script>
  131. </body>
  132. </html>
Javajspservletsjstl

1条答案

按热度按时间
rseugnpd

rseugnpd1#

有很多代码需要理解，但我想说的是问题在于：

  1. <foreach>
  2.   <form>
  3.     <c:set var="purchaseCar" value="${car}" scope="application" />
  4.  <submit...
  5. </form>
  6. </foreach>

这里的会话范围就足够了。但真正的问题是，它对所有记录都执行，并且每个记录都覆盖了前一个记录。因此purchasecar变量在每次迭代中都会被修改。
通常以你想要的形式 <input> 将所需信息与请求一起发送到servlet的标记。通常是车的id:）

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