JSP为request.getParameter（）返回null，但在EL中显示值

Question

I am new to servlets and JSPs. Recently.. I have been trying to send data from my Servlet to JSP using requestDispatcher.

This is my Servlet code responsible:

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

        sampleClass sampleObject = new sampleClass(1, "myname");
        ObjectMapper mapper = new ObjectMapper();
        String jsonstring = mapper.writeValueAsString(sampleObject);
        request.setAttribute("values", jsonstring);
        request.setAttribute("valuees", "testing");
        request.getRequestDispatcher("/somejsp").forward(request, response);
    }

My JSP part responsible for retrieving data:

${values}
${valuees}
<% 
    //out.println(Message);
    Enumeration enume = request.getParameterNames();
    for (Entry<String, String[]> entry : request.getParameterMap().entrySet()) {
        String name = entry.getKey();
        String value = entry.getValue()[0];
        // ...
    }
    String value = request.getParameter("values");
    out.println(value);
    String valuee = request.getParameter("valuees");
    out.println(valuee);
 %>

But the output I get is:

{"n":1,"name":"myname"} testing null null

as you can see both the EL gives correct output, the implementation with the Enumeration returns nothing and the other two return null.

I donot understand this. I couldn't find any solution online.

Answer 1

您会将属性 （选择存储在请求中的任何对象，使用您选择的名称）与参数 （浏览器作为请求的一部分发送的字符串，如foo=bar&baz=2 。