package com.imooc.servlet;

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

public class AddServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String i=req.getParameter("num");
        int n=Integer.parseInt(i);
        int sum=0;
        for(int p=0;p<=n;p++){
            sum=sum+p;
        }
        String html="<h1 style='color:red'>"+sum+"</h1>";
        PrintWriter out=resp.getWriter();
        out.println(html);
    }
}

<servlet>
    <servlet-name>add</servlet-name>
    <servlet-class>com.imooc.servlet.AddServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>add</servlet-name>
    <url-pattern>/addPlus</url-pattern>
</servlet-mapping>

相关截图：