Servlet request.getParameter()总是返回"null"

Question

我已经阅读了所有相关问题,尝试了每个接受的答案,但我仍然没有找到运气.

我有一个在tomcat上运行的网站,有一个子页面/ Demo /,它有四个文本字段和一个Submit按钮.提交按钮如下所示

 <form method="post" action="DemoServlet">
                 <input type="hidden" name="form_action" value="write" />
                 <table>
                    <tr>
                       <td>
                          First Name:
                       </td>
                       <td>
                          <input type="text" 
                             name="firstname" />
                       </td>
                    </tr>
                    <tr>
                       <td>
                          Last Name:
                       </td>
                       <td>
                          <input type="text" 
                             name="lastname" id = "lastname" />
                       </td>
                    </tr>
                    <tr>
                       <td>
                          Email:
                       </td>
                       <td>
                          <input type="text" 
                             name="recipient" />
                       </td>
                    </tr>
                    <tr>
                       <td>
                          Phone1:
                       </td>
                       <td>
                          <input type="text" 
                             name="phone" />
                       </td>
                    </tr>
                    <tr>
                       <td>
                          <input type=button onClick="location.href='../demo-servlet'" value='Submit'/>
                       </td>
                       <td>
                       </td>
                 </table>
              </form>

这个/ demo-servlet在web.xml中指定如下

 <servlet>
    <servlet-name>DemoServlet</servlet-name>
    <servlet-class>PACKAGENAME.DemoServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>DemoServlet</servlet-name>
    <url-pattern>/demo-servlet</url-pattern>
</servlet-mapping>

该servlet如下所示

protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {

    // Retrieve First Name from /Demo/ text field
    firstName = request.getParameter("firstname");

    // Retrieve Last Name from /Demo/ text field
    lastName = request.getParameter("lastname");
    /* MORE CODE HERE */
    request.getRequestDispatcher("/WEB-INF/confirmation.jsp").forward(request, response);
}

然后转发到我的confirmation.jp文件,显示该进程已成功.

我的问题是,变量和两者都在调用request.getParameter()函数后返回值"null".

任何人都知道为什么会这样？

Answer 1

表单标记上的方法是post,但您已在servlet中实现了doGet.你的表单标签上的动作也是DemoServlet,但应该像../demo-servlet 你可能根本不需要onClick.