为什么我的服务器运行出现 http 500 的错误啊  跟着老师的打的

求高手来解救下，架包用的gson-2.2.2.jar

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 this.doPost(request, response);
 }

 /**
  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
  */
 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  response.setContentType("text/html;charset=utf-8");
  
  PrintWriter out=response.getWriter();
  
  data data = new data();

  ArrayList<Person> personslist = new ArrayList<Person>();
  ArrayList<schoolinfor> schoolinforslist = new ArrayList<schoolinfor>();

  // 写入json数据
  Person person1 = new Person();
  person1.setName("小华");
  person1.setAddress("新华街22号");

  schoolinfor schoolinfor1 = new schoolinfor();
  schoolinfor1.setMiddleSchool("第一初中");
  schoolinfor1.setCollege("清华大学");

  person1.setSchoolinfor(schoolinfor1);
  personslist.add(person1);
  schoolinforslist.add(schoolinfor1);
  // **************************************************************
  Person person2 = new Person();
  person2.setName("小明");
  person2.setAddress("中华街22号");

  schoolinfor schoolinfor2 = new schoolinfor();
  schoolinfor2.setMiddleSchool("第二初中");
  schoolinfor2.setCollege("北京大学");

  person2.setSchoolinfor(schoolinfor2);
  personslist.add(person2);
  schoolinforslist.add(schoolinfor2);

  data.setPersonlist(personslist);
  data.setSchoollist(schoolinforslist);
  // 转为json数据格式
  Gson gson=new Gson();
  out.println(gson.toJson(data));
 }

}