Question

request.getParamter（）方法应返回类型参数值，但它返回空值。

@Override
   public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
           throws IOException, ServletException {

       HttpServletRequest req = (HttpServletRequest) request;
       HttpServletResponse resp = (HttpServletResponse) response;

       String action = req.getParameter("type");

       if(action != null && controllerMapping.containsKey(action)) {
           config.getServletContext().getRequestDispatcher(controllerMapping.get(action)).forward(req, resp);
       }
       else {
           chain.doFilter(request, response);
       }
   }

呼叫页面在这里：

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Add an Athlete</title>
        <link href="<c:url value='/css/main.css' />" type="text/css" rel="stylesheet" />
    </head>
    <body>
        <div class="add_athlete">
            <fieldset>
                <legend> Athlete Information </legend>
                <form class="add_athlete" action="<c:url value='/' />" method="post" enctype="multipart/form-data">
                    <input type="hidden" name="type" value="add_athlete" />
                    <label>First Name:</label>
                        <input type="text" name="first_name" placeholder="Enter First Name" required="required"/>
                    <label>Last Name:</label>
                        <input type="text" name="last_name" placeholder="Enter Last Name" required="required"/>
                    <label>Age:</label>
                        <input type="number" name="age" placeholder="Enter Age" required="required" />
                    <label>Email:</label>
                        <input type="email" name="email" placeholder="Enter Email Address" required="required" />
                    <label>Image:</label>
                        <input type="file" name="file" required="required" /><br />
                        <input type="submit" name="submit" value="Submit" />
                </form>
            </fieldset>
        </div>
    </body>
</html>

当我在servlet的doPost（）方法中使用类型param时，它可以正常工作，但是当此请求转发到servlet的doFilter（）方法时，我收到NullPointerException。是因为POST方法吗？我不明白为什么它不起作用，有人可以帮我解决吗？

HttpRequest.getParameter（“ ...”）在doFilter方法中不返回值

0 个答案: