无法访问-提示localhost拒绝连接请求

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
   <form action="servlet-advanced/ns">
       <input type="text" name="num" placeholder="请输入100以内的数字">
       <input type="submit" value="求累加和">
   </form>
</body>
</html>

package com.imooc.servlet;

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 numberSum
*/
@WebServlet("/ns")
public class numberSum extends HttpServlet {
   private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public numberSum() {
        super();
        // TODO Auto-generated constructor stub
    }

   /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
   protected void doGet(HttpServletRequest request, HttpServletResponse response)
           throws ServletException, IOException {
       String num=request.getParameter("num");
       int sum=0;
       for(int i=1;i<=Integer.parseInt(num);i++) {
           sum+=i;
       }
       request.setAttribute("result", sum);
       request.getRequestDispatcher("/nr").forward(request, response);
   }

}

package com.imooc.servlet;

import java.io.IOException;
import java.io.PrintWriter;

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 numResult
*/
@WebServlet("/nr")
public class numResult extends HttpServlet {
   private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public numResult() {
        super();
        // TODO Auto-generated constructor stub
    }

   /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       String num=request.getParameter("num");
       String result=request.getAttribute("result").toString();
       PrintWriter out=response.getWriter();
       out.println("<h1>"+num+"累加和为："+result+"<h1/>");
   }

}