@RequestParam 为空（Spring MVC）答案

【问题标题】：@RequestParam is null (Spring MVC)@RequestParam 为空（Spring MVC）
【发布时间】：2012-07-02 10:17:08
【问题描述】：

我正在尝试向我的网络应用程序添加一个编辑功能，但我在使用 @RequestParam 时遇到了一些问题。它得到的参数是 null ，它不应该是。我希望有人能指出我在哪里犯了错误。

以下是控制器的方法：

@RequestMapping(value = "/edit", method = RequestMethod.GET)
public String getEdit(@RequestParam("customerId") Integer customerId, Model model) {
Customer existingCustomer = customerService.retrieveCustomer(customerId);
    model.addAttribute("customerAttribute", existingCustomer);
    return "edit-customer";
}

@RequestMapping(value = "/edit", method = RequestMethod.POST)
public String postEdit(@RequestParam("customerId") Integer customerId,
        @ModelAttribute("customerAttribute") @Valid Customer customer, BindingResult result) {
    if (result.hasErrors()) {
        return "edit-customer";
    }
    customer.setCustomerId(customerId);
    customerService.editCustomer(customer);
    return "redirect:/test/customer/list";

还有两个jsp页面

edit-customer.jsp：

<body>

<h1>Edit Existing Customer</h1>

<c:url var="saveUrl" value="/test/customer/edit?customerId=${customerAttribute.customerId}" />
<form:form modelAttribute="customerAttribute" method="POST" action="${saveUrl}">
 <table>
  <tr>
   <td><form:label path="customerId">Customer Id:</form:label></td>
   <td><form:input path="customerId" disabled="true"/></td>
  </tr>

  <tr>
   <td><form:label path="customerCountry">Customer Country</form:label></td>
   <td><form:input path="customerCountry"/></td>
  </tr>

  <tr>
   <td><form:label path="customerName">Customer Name:</form:label></td>
   <td><form:input path="customerName"/></td>
  </tr>

 </table>

 <input type="submit" value="Save" />
</form:form>

</body>

查看所有客户.jsp：

<body>
<a href="<c:url value="/test/home"/>">Home</a>

<h1>Customers</h1>

<c:url var="addUrl" value="/test/customer/add" />
<c:url var="editUrl" value="/test/customer/edit?customerId=${customer.customerId}"/>
<c:if test="${!empty customers}">
<a href="${addUrl}">Add</a> 
</c:if>
<table style="border: 1px solid; width: 500px; text-align:center">
 <thead style="background:#ccc">
  <tr>
   <th>Customer Id</th>
   <th>Customer Country</th>
   <th>Customer Name</th>
   <th colspan="4"></th>
  </tr>
 </thead>
 <tbody>
 <c:forEach items="${customers}" var="customer">
  <tr>
   <td><c:out value="${customer.customerId}" /></td>
   <td><c:out value="${customer.customerCountry}" /></td> 
   <td><c:out value="${customer.customerName}" /></td>
   <td><a href="${editUrl}">Edit</a></td>
  </tr>
 </c:forEach>
 </tbody>
</table>

<c:if test="${empty customers}">
 There are currently no customers in the list. <a href="${addUrl}">Add</a> a customers.
</c:if>

</body>

谁能看到为什么GET 方法中的Integer customerId 为空？

谢谢你， D

【问题讨论】：

标签： java spring model-view-controller jsp spring-mvc

【解决方案1】：

您在初始化之前使用${customer.customerId}：

<!-- you use it here -->
<c:url var="editUrl" value="/test/customer/edit?customerId=${customer.customerId}"/>
<c:if test="${!empty customers}">
....
 <tbody>
 <!-- and initialize it here -->
 <c:forEach items="${customers}" var="customer">
  <tr>
   <td><c:out value="${customer.customerId}" /></td>
   <td><c:out value="${customer.customerCountry}" /></td> 
   <td><c:out value="${customer.customerName}" /></td>
   <td><a href="${editUrl}">Edit</a></td>
  </tr>
 </c:forEach>
 </tbody>
</table>

只需在循环内设置editUrl：

<c:if test="${!empty customers}">
....
 <tbody>
 <c:forEach items="${customers}" var="customer">
   <c:url var="editUrl" value="/test/customer/edit?customerId=${customer.customerId}"/>
  <tr>
   <td><c:out value="${customer.customerId}" /></td>
   <td><c:out value="${customer.customerCountry}" /></td> 
   <td><c:out value="${customer.customerName}" /></td>
   <td><a href="${editUrl}">Edit</a></td>
  </tr>
 </c:forEach>
 </tbody>
</table>

它应该可以工作。无论如何，您都必须为每个客户重置 editUrl。

【讨论】：

谢谢你的问题:)

【解决方案2】：

这可能是因为您将 customerId 接受为 Integer，请尝试将其接受为 String。试试这个：

@RequestMapping(value = "/edit", method = RequestMethod.GET)
public String getEdit(@RequestParam("customerId") String customerId, Model model) {
Customer existingCustomer = customerService.retrieveCustomer(Integer.parseInt(customerId));
    model.addAttribute("customerAttribute", existingCustomer);
    return "edit-customer";
}

@RequestMapping(value = "/edit", method = RequestMethod.POST)
public String postEdit(@RequestParam("customerId") String customerId,
        @ModelAttribute("customerAttribute") @Valid Customer customer, BindingResult result) {
    if (result.hasErrors()) {
        return "edit-customer";
    }
    customer.setCustomerId(Integer.parseInt(customerId));
    customerService.editCustomer(customer);
    return "redirect:/test/customer/list";

【讨论】：