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，

　　使用这种方式接收可以接收

1 1 @RequestMapping(value = "/insertUser", method = RequestMethod.POST)
2 2 public ResultT insertUser(@RequestBody Map<String,List<User>> map){
3 3     List<User> userList = map.get("insertUserList");  
4 4 }
5 5 
6 6 //前台json格式
7 7 {
8 8     "insertUserList": [
9 9         {
1010             "firstName": "Brett",
1111             "lastName": "McLaughlin",
1212             "email": "aaaa"
1313         },
1414         {
1515             "firstName": "Jason",
1616             "lastName": "Hunter",
1717             "email": "bbbb"
1818         },
1919         {
2020             "firstName": "Elliotte",
2121             "lastName": "Harold",
2222             "email": "cccc"
2323         }
2424     ]
2525 }