老师这什么情况啊?我都搞不清我错在哪里了?复制您的代码过来都在浏览器上运行不了

package com.imooc.ajax;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.alibaba.fastjson.JSON;

/**
* Servlet implementation class Dpart
*/
@WebServlet("/Dpart")
public class Dpart extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  response.setCharacterEncoding("utf-8");
  List<String > department =new ArrayList<>();
  List<String > employee = new ArrayList<>();
  List<String > position =new ArrayList<>();

  department.add("人事部");
  department.add("市场部");
  department.add("研发部");

  employee.add("张三丰");
  employee.add("杨过");
  employee.add("黄老邪");

  position.add("工程师");
  position.add("经理");
  position.add("董事长");

  String flag=request.getParameter("flag");
  int a =Integer.parseInt(flag);

  if(a==1){
   String json =JSON.toJSONString(employee);
   response.getWriter().println(json);
  }else if(a==2){
   String json =JSON.toJSONString(employee);
   response.getWriter().println(json);
  }else{
   String json=JSON.toJSONString(position);
   response.getWriter().println(json);
  }

}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<style type="text/css">
#all{
     width: 600px;
     height: 50px;
     background-color: #D0D0D0;
     margin: auto;
}

.b{
    width: 196px;
    height: 50px;
    margin: auto;
    background-color: #F0F0F0;
    font-size: 15px;
}

#list{
    width: 600px;
    height: 600px;
    text-align: center;
    font-size: 20px;
    background-color: #F0F0F0;
    margin: auto;
}
</style>
</head>

<body>
     <div id="all">
         <button class="b" id="emp" onclick="check(1)">员工列表</button>
         <button class="b" id="depart" onclick="check(2)">部门列表</button>
         <button class="b" id="postion" onclick="check(3)">职位列表</button>
    </div>
         <div id="list"></div>

         <script type="text/javascript">
                   //创建XMLHttpRequest对象
                   var xmlhttp ;
                   if(window.XMLHttpRequest){
                       xmlhttp = new XMLHttpRequest();
                   }

                  //实现员工列表
                 function check(falg){
                   //发送Ajax请求
                   xmlhttp.open("GET","/Ajax/Dpart?flag="+falg,true);
                   xmlhttp.send();
                   //处理服务器响应
                   xmlhttp.onreadystatechange = function(){
                       if(xmlhttp.readyState == 4 && xmlhttp.status == 200){
                           //获取响应文本
                           var text = xmlhttp.responseText;
                           var json = JSON.parse(text);
                           console.log(json);
                           var html = "";
                           for(var i = 0; i < json.length; i ++){
                               var emp = json[i];
                               html = html + "<h3>" + emp + "</h3>";
                               document.getElementById("list").innerHTML = html;
                           }
                       }
                   }

               }


         </script>
</body>

</html>