servlet写完了， add/remove我点击后有提示，我哪里错了啊

<?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>Firstser</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>

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 FirstServlet

 */

@WebServlet("/FirstServlet")

public class FirstServlet extends HttpServlet {

@Override

protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//接收请求发来的参数

String name=request.getParameter("name");

String html="<h1 style='color:red'>hi,"+name+"!</h1><hr/>";

System.out.println("返回给浏览器的响应数据为："+html);

PrintWriter out=response.getWriter();

out.println(html);//将html发送回浏览器

}

}