Question

我在Spring MVC / Maven Web应用程序中的方法调用上遇到Null异常错误。我在方法中使用PagedListHolder从MySQL数据库中检索16个产品的页面中的产品。 Web应用程序在我的Live Centos 6 VPS上工作正常，但现在给我一个Null异常错误。完全相同的程序在我的Eclipse Mars测试环境中完美运行。

下面是一些Stack Trace和相关代码。希望有人可以为我解释这个问题。

谢谢和问候， Gus Hayes

堆栈跟踪

HTTP状态500 - 请求处理失败;嵌套异常是java.lang.NullPointerException

输入例外报告

消息请求处理失败;嵌套异常是java.lang.NullPointerException

说明服务器遇到内部错误，导致无法完成此请求。

例外

org.springframework.web.util.NestedServletException：请求处理失败;嵌套异常是java.lang.NullPointerException org.springframework.web.servlet.FrameworkServlet.processRequest（FrameworkServlet.java:978） org.springframework.web.servlet.FrameworkServlet.doPost（FrameworkServlet.java:868） javax.servlet.http.HttpServlet.service（HttpServlet.java:648） org.springframework.web.servlet.FrameworkServlet.service（FrameworkServlet.java:842） javax.servlet.http.HttpServlet.service（HttpServlet.java:729） org.apache.tomcat.websocket.server.WsFilter.doFilter（WsFilter.java:52） net.sourceforge.pagesdialect.ExportFilter.doFilter（ExportFilter.java:52）

根本原因

显示java.lang.NullPointerException com.thestoreyard.app.controllers.StoreController.clientsNavigateToPage（StoreController.java:77） sun.reflect.GeneratedMethodAccessor106.invoke（未知来源） sun.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43） java.lang.reflect.Method.invoke（Method.java:606） org.springframework.web.method.support.InvocableHandlerMethod.doInvoke（InvocableHandlerMethod.java:221）

商店控制器

// List of Products by Category ID, paginated
@RequestMapping(value = "/category", method = RequestMethod.GET)
public String category(HttpServletRequest request, @RequestParam("id") Byte id, ModelMap mm) {
    PagedListHolder pagedList = new PagedListHolder(productService.getByCategoryId(id));
    pagedList.setPageSize(16);
    request.getSession().setAttribute("productList", pagedList);
    mm.put("productList", pagedList.getPageList());
    mm.put("categoryList", categoryService.getAll());
    mm.put("id", id);
    return "store_catalog/products";
}

// The logic for pagination
@RequestMapping(value = "/categoryNav", method = RequestMethod.POST)
public String clientsNavigateToPage(HttpServletRequest request, ModelMap mm,
                                    @RequestParam String action) {

    PagedListHolder pagedList = (PagedListHolder) request.getSession().getAttribute("productList");

    if (action.equals("next")) {
        pagedList.nextPage();

    } else if (action.equals("previous")) {
        pagedList.previousPage();
    }

    mm.put("productList", pagedList.getPageList());
    mm.put("categoryList", categoryService.getAll());
    return "store_catalog/products";
}

 // The product spec page by product ID
 @RequestMapping(value = "/product", method = RequestMethod.GET)
    public String product(@RequestParam("id") Integer id, ModelMap mm) {
        mm.put("productSpec", productService.getById(id));
        mm.put("categoryList", categoryService.getAll());
        mm.put("id", id);
        return "store_catalog/productspec";
 }

products.html放在

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:th="http://www.thymeleaf.org"
xmlns:pages="http://www.thymeleaf.org/pagesdialect"
xmlns:layout="http://www.ultraq.net.nz/web/thymeleaf/layout">

<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta name="description" content="The Store Yard - Portlaoise, Co. Laois" />
    <meta name="author" content="The Store Yard" />

    <link href="resources/css/bootstrap.min.css" th:href="@{/resources/css/bootstrap.min.css}" rel="stylesheet" />
    <link rel="stylesheet" type="text/css" media="all" href="resources/css/style.css" th:href="@{/resources/css/style.css}" />
    <script type="text/javascript" src="resources/css/jquery.js" th:href="@{/resources/css/jquery.js}"></script>
    <link type="text/css" rel="stylesheet" th:href="@{/resources/css/magiczoom.css}"/>
    <script type="text/javascript" th:src="@{/resources/css/magiczoom.js}"></script>

    <title>The Store Yard - Portlaoise, Co. Laois</title>

</head>

<body>
<div id="header">

  <div id="social">
  <a href="https://www.facebook.com/the-storeyard-Portlaoise-134807199880399/"><img src="resources/css/images/facebook.png" th:href="@{/resources/css/images/facebook.png}" alt="facebook" width="26" height="26" border="0" /></a>
  <a href="https://twitter.com/thestoreyard"><img src="resources/css/images/twitter.png" th:href="@{/resources/css/images/twitter.png}" width="26" height="26" alt="twitter" /></a>
  <a href="mailto:info@thestoreyard.ie"><img src="resources/css/images/email.png" th:href="@{/resources/css/images/email.png}" alt="email" width="26" height="26" border="0" /></a>
</div>
</div>

<ul class="dropdown"><!-- menu -->

<li><a href="home.html" th:href="@{/}">Home</a></li>
<li><a href="about.html">About Us</a></li>
<li><a href="categories.html" th:href="@{/categories}">Products</a></li>
<li><a href="store.html">Gallery</a>
<ul class="sub_menu">
    <li><a href="store.html">Venue Hire</a></li>
    <li><a href="media.html">In The Media</a></li>      
    <li><a href="music.html">Music @ The Store Yard</a></li>
    <li><a href="films.html">Film Sets</a></li>
    <li><a href="tynans.html">Tynans Restaurant</a></li>
</ul>

</li>

<!-- end submenu -->
<li><a href="location.html">Our Location</a></li>
<li><a href="contact.html">Contact Us</a></li>

</ul><!-- close menu -->

<div id="content">
  <!-- content -->
   <!--  <h1 th:class="${id} == ${category.id} ? 'active'" th:text="${#strings.toUpperCase(category.name)}"></h1> -->

   <br></br>

         <div class="col-xs-12 col-md-3" th:each="product : ${productList}">

                        <div class="thumbnail">



                    <a th:href="@{/product(id=${product.id})}"><img class="img-responsive"
                         th:src="@{|/resources/image_upload/products/${product.name}.jpg|}"></img></a>           
                            <div class="caption">
                                <p>
                                    <b>Name:</b> <span th:text="${product.name}"></span>
                                </p>
                                <p>
                                    <b>Price:</b> <span th:text="|${product.price} Euro|"></span>
                                </p>


                            </div>

                        </div>

                        </div>



         <form id="mainform" class="basic-grey" method="post" action="/categoryNav" th:action="@{/categoryNav}">
                <input type="submit" name="action" value="previous" class="btn btn-info" />
                <input type="submit" name="action" value="next" class="btn btn-info" />

            </form>


</div>

<div id="sidebar"><!-- sidebar -->

<h3>Categories</h3>

    <div class="navcontainer">
    <ul class="nav nav-pills nav-stacked">
        <li th:each="category : ${categoryList}" th:class="${id} == ${category.id} ? 'active'">
            <a th:href="@{/category(id=${category.id})}" th:text="${#strings.toUpperCase(category.name)}"></a>
        </li>
    </ul>
    </div>


</div><!-- end sidebar -->

<div id="footer"> 
  <div align="center">
    <p><a href="home.html" th:href="@{/}">Home</a> | <a href="about.html">About</a> | <a href="categories.html">Products</a> | <a href="store.html">Gallery</a> | <a href="location.html">Our Location</a> | <a href="contact.html">Contact</a> |</p>


    <div class="footerimageleft"><img src="resources/css/images/irishtimes2.jpg" th:href="@{/resources/css/images/irishtimes2.jpg}" /></div>


    <div class="footerimageright"><img src="resources/css/images/iada2.jpg" th:href="@{/resources/css/images/iada2.jpg}" /></div>




    <p><h2>Office:+353 (0)57 86 80088</h2></p>
    <br />
    <p>&copy;2016 - The Store Yard</p>
  </div>
</div>

</body>
</html>

ProductService.java

    package com.thestoreyard.app.service;

import com.thestoreyard.app.dao.ProductDao;
import com.thestoreyard.app.domain.Product;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import javax.annotation.Resource;
import java.util.List;

@Service
@Transactional
public class ProductService {

    @Resource
    private ProductDao productDao;

    public List<Product> getByCategoryId(Byte id) {
        return productDao.findByCategoryId(id);
    }

    public Product getById(Integer id) {
        return productDao.findOne(id);
    }




}

在方法中使用PagedListHolder时出现Null Exception错误

0 个答案: