request.setAttribute 里面参数问题

package chp1.action;
import chp1.framework.*;
import javax.servlet.http.*;
import chp1.biz.*;

public class AddAction implements Action{
private Calculator biz = new Calculator();
public String execute(HttpServletRequest request,HttpServletResponse response){
double num1 = Double.parseDouble(request.getParameter("num1"));
double num2 = Double.parseDouble(request.getParameter("num2"));
double result = biz.add(num1, num2);

request.setAttribute("result",result);//这里报错
return "/add_result.jsp";
}

}

biz 方法public class Calculator {
public double add(double a,double b){
return a+b;
}
//接口public interface Action {
public String execute(HttpServletRequest request,HttpServletResponse response);
}
//Servlet public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, I

Request、Request.Form和Request.QueryString相同点 require&request request 问题 request.servervariables Request.QueryString[] jsp request request.setAttribute request.getParameter() Request.ServerVariables reQuest.Querystring???