麻烦老师看一下我这个哪里错了

我就这两个文件来处理，但无响应，是哪里错了呀，这个思路可行吗

<%@ page language="java" contentType="text/html;charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
   <head>
       <meta charset="UTF-8">
       <title>这是职员列表</title>
   </head>
   <body>
       <div style="width:1000px;">
           <button style="width:300px;">员工列表</button>
           <button style="width:300px;">职位列表</button>
           <button style="width:300px;">部门列表</button>
       </div>
       <div id="outstr" style="width:1000px;text-align:center;">
           
       </div>
       <script type="text/javascript">
           //获得三个按钮button的数组bList
           var bList=document.getElementsByTagName("button");
           var outstr=document.getElementById("outstr");
           for(var i=0;i<bList.length;i++){
               bList[i].onclick=function(){
                   var xmlhttp;
                   if(window.XMLHttpRequest){
                       xmlhttp=new XMLHttpRequest();
                   }else{
                       xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
                   }
                   var url="/ajax/emp_servlet?num=";
                   url=url+i;
                   xmlhttp.open("GET",url,true);
                   url="";
                   xmlhttp.send();
                   xmlhttp.onreadystatechange=function(){
                       if(xmlhttp.readyState==4 && xmlhttp.status==200){
                           var t = xmlhttp.responseText;
                           document.getElementById("outstr").innerHTML=t;
                       }
                   }
               }
           }
       </script>
   </body>
</html>

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;

/**
* Servlet implementation class empListServlet
*/
@WebServlet("/emp_servlet")
public class empListServlet extends HttpServlet {
   private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public empListServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

   /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       response.setContentType("text/html;charset=UTF-8");
       String i=request.getParameter("num");
       List<String> list=new ArrayList<String>();
       if(i.equals("0")) {
           list.add("小红");
           list.add("小明");
           list.add("小白");
       }else if(i.equals("1")) {
           list.add("职员");
           list.add("经理");
       }else {
           list.add("人事部");
           list.add("技术部");
           list.add("无线支持部");
       }
       String outstr="";
       for(var str:list) {
           outstr+="<h3>"+str+"</h3>";
       }
       response.getWriter().println(outstr);
   }
}