老师帮忙看一下

ComputerServlet.java

package com.superj.servlet;
 
import java.io.IOException;
import java.io.PrintWriter;
 
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
public class ComputerServlet extends HttpServlet{
 
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String n = req.getParameter("n");
        int n1 = Integer.parseInt(n);
        int num = n1*(n1+1)/2;
        PrintWriter out = resp.getWriter();
        out.println("<p style='color:red'>"+num+"</p>");//将html发送回浏览器
    }
     
}

web.xml

<?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>ServletProj</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>shop</servlet-name>
      <servlet-class>com.superj.servlet.ServletProj</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>shop</servlet-name>
      <url-pattern>/ShopServlet</url-pattern>
  </servlet-mapping>
    <servlet>
      <servlet-name>computer</servlet-name>
      <servlet-class>com.superj.servlet.ComputerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>computer</servlet-name>
      <url-pattern>/ComputerServlet</url-pattern>
  </servlet-mapping>
</web-app>