Question

我有一个.jsp文件，它通过post方法将数据发送到servlet，但是当我尝试通过request.getAttribute（）访问servlet中的数据时，它打印出“null”

我的.jsp文件如下所示：

            <form name="update" action="UpdateServlet" method="post"
            accept-charset="utf-8">
            <label>Name:</label><input type="text" name="input_name"    id="input_name"><br>
            <label>Beschreibung:</label> <input type="text" name="input_beschreibung" id="input_beschreibung"><br>
            <input type="hidden" name="input_id" id="input_id">
            <input type="submit" value="Okay">
            <button type="button" onclick="closeDialog()">Abbrechen</button>
            </form>

我的servlet看起来像这样：

public class UpdateServlet extends HttpServlet {

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html");

    System.out.println((String)request.getAttribute("input_id"));
    System.out.println((String)request.getAttribute("input_name"));
    System.out.println((String)request.getAttribute("input_beschreibung"));

    RequestDispatcher rd=request.getRequestDispatcher("LoadServlet");  
    rd.forward(request, response);

}

web.xml的一部分：

  <servlet>
  <servlet-name>UpdateServlet</servlet-name>
  <servlet-class>wochenplaner.UpdateServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  <servlet-name>UpdateServlet</servlet-name>
  <url-pattern>/UpdateServlet</url-pattern>
  </servlet-mapping>

我不明白为什么请求的属性为空。提前谢谢！

Answer 1

您感到困惑request.getAttribute("")和request.getParameter("")。你需要使用后者：

public class UpdateServlet extends HttpServlet {

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html");

    System.out.println(request.getParameter("input_id"));
    System.out.println(request.getParameter("input_name"));
    System.out.println(request.getParameter("input_beschreibung"));

    RequestDispatcher rd=request.getRequestDispatcher("LoadServlet");  
    rd.forward(request, response);

}

请参阅此处进行进一步讨论：

https://stackoverflow.com/a/5243833/1356423

Answer 2

试试这个：

request.getParameter("input_id");

Answer 3

您应该使用request.getParameter()而不是request.getAttribute()

Difference between getAttribute() and getParameter()

从request.getAttribute（）

3 个答案: