jsp接收不到servlet传的数据，怎么解决？

servlet类：
package Control;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**

Servlet implementation class Demoo
*/
@WebServlet(name="Demoo",urlPatterns = { "/Demoo"})
public class Demoo extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
```
String a="aaaaaaa";
request.setAttribute("aa",a);
request.getRequestDispatcher("a.jsp").forward(request, response);
```
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//doGet(request, response);
}

}

jsp：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ page import="Beans.*,java.util.*"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

<!DOCTYPE html>

Insert title here

    <p>传值：</p>
    <p>${aa}</p>
    <%=request.getAttribute("aa")%>

原理上来讲，用法是没有错的，需要排除一下是不是用了框架，页面两个地方都没有数值吗？