老师这是为什么

package com.imooc.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 FirstServlet extends HttpServlet {
 @Override
 protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  String name=request.getParameter("name");
  String html="<h1 style='color=yellow'>hi,"+name+"!</h1><hr/>";
  System.out.println("返回给浏览器的相应数据为："+html);
  PrintWriter out=response.getWriter();
  out.println(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_4_0.xsd" id="WebApp_ID" version="4.0">
  <display-name>FirstServlet</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>first</servlet-name>
    <servlet-class>com.imooc.servlet.FirstServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>first</servlet-name>
    <url-pattern>/hi</url-pattern>
  </servlet-mapping>
 
</web-app>