java - Map的订单输出

Question

编写REST API，请求和响应都是Json。我将 json 响应作为 Map 进行处理，并想知道为什么它在屏幕上的输出不是按照我制作的顺序排列的？我的 Controller 的示例代码，我在其中构建 map :

@ExceptionHandler(ApiErrorNotFound.class)
@ResponseStatus(value = HttpStatus.NOT_FOUND)
public @ResponseBody Map handleDaoException(HttpServletRequest req, ApiErrorNotFound exc) {
    Map<String, String> res = new HashMap<>();
    Date date = new Date();
    res.put("timestamp", String.valueOf(new Timestamp(date.getTime())));
    res.put("status", String.valueOf(exc.getStatus()));
    res.put("error", "Not Found");
    res.put("exception", ApiErrorNotFound.class.getName());
    res.put("message", exc.getMessage());
    res.put("path", req.getServletPath());
    return res;
}

输出是:

{
  "exception": "com.zzheads.HomeAutomation.exceptions.ApiErrorNotFound",
  "path": "/room/9",
  "error": "Not Found",
  "message": "Can't find room with 9 id. (com.zzheads.HomeAutomation.controller.RoomController.getRoomById(RoomController.java:63))",
  "timestamp": "2016-08-21 15:49:01.961",
  "status": "404"
}

Answer 1

不保证HashMap的迭代顺序与插入顺序相同。

如果你想在迭代时保持插入顺序，请查看:

LinkedHashMap