2-6看看完美不？

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="/ServletPractice1/sum">
<input style="text" name="num" placeholder="请输入100以内的数字">
<button style="sbumit">求累加和</button>
</form>
</body>
</html>

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>ServletPractice1</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
  <servlet-name>sum</servlet-name>
  <servlet-class>com.system.sum.SumRequest</servlet-class>
  </servlet>
  
  <servlet-mapping>
  <servlet-name>sum</servlet-name>
  <url-pattern>/sum</url-pattern>
  </servlet-mapping>
</web-app>

package com.system.sum;

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 SumRequest
 */
@WebServlet("/SumRequest")
public class SumRequest extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SumRequest() {
        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 num1=Integer.parseInt(num);
		System.out.println("从转发中获取到的数字为："+num);
		int sum=0;
		for(int i=0;i<=num1;i++) {
			sum=sum+i;
		}
		request.setAttribute("sum",sum);
		System.out.println("所求累加和为："+sum);
		request.getRequestDispatcher("/SumShow").forward(request,response);
	}


}

package com.system.sum;

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 SumShow
 */
@WebServlet("/SumShow")
public class SumShow extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public SumShow() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		int sum=(int) request.getAttribute("sum");
		System.out.println("request获得的sum的值为："+sum);
		response.getWriter().println(sum);
	}

}