java后台接收json数据，报错com.alibaba.fastjson.JSONObject cannot be cast to xxx

　　从前台接收json封装的list数据，在后台接收时一直报错，com.alibaba.fastjson.JSONObject cannot be cast to xxx，

　　使用这种方式接收能够接收

 1 @RequestMapping(value = "/insertUser", method = RequestMethod.POST)  2 public ResultT insertUser(@RequestBody Map<String,List<User>> map){  3     List<User> userList = map.get("insertUserList");  4 }  5 
 6 //前台json格式
 7 {  8     "insertUserList": [  9  { 10             "firstName": "Brett", 11             "lastName": "McLaughlin", 12             "email": "aaaa"
13  }, 14  { 15             "firstName": "Jason", 16             "lastName": "Hunter", 17             "email": "bbbb"
18  }, 19  { 20             "firstName": "Elliotte", 21             "lastName": "Harold", 22             "email": "cccc"
23  } 24  ] 25 }