java8 listmap聚合后内容顺序不变

学习了groupingBy的用法，在处理List<Map>的数据，顺序会发生变化：

直接聚合

public static void main(String[] args){String data = "[{\"codeType\":\"ALRAM\",\"code\":\"1\",\"name\":\"普通告警\",\"sortId\":\"1\"},{\"codeType\":\"ALRAM\",\"code\":\"2\",\"name\":\"中级告警\",\"sortId\":\"2\"},{\"codeType\":\"ALRAM\",\"code\":\"3\",\"name\":\"严重告警\",\"sortId\":\"3\"},{\"codeType\":\"ALRAM\",\"code\":\"4\",\"name\":\"特级告警\",\"sortId\":\"4\"},{\"codeType\":\"NOTICE\",\"code\":\"1\",\"name\":\"短信通知\",\"sortId\":\"1\"},{\"codeType\":\"NOTICE\",\"code\":\"2\",\"name\":\"邮箱通知\",\"sortId\":\"2\"},{\"codeType\":\"NOTICE\",\"code\":\"3\",\"name\":\"微信消息通知\",\"sortId\":\"3\"}]";JSONArray items = JSON.parseArray(data);Map<String, List<JSONObject>> codeType = ListUtils.emptyIfNull(items).stream().map(e -> (JSONObject) e).collect(Collectors.groupingBy(e -> MapUtils.getString(e, "codeType")));System.out.println(JSON.toJSONString(codeType));}

结果：

{"NOTICE": [{"code": "1","codeType": "NOTICE","sortId": "1","name": "短信通知"}, {"code": "2","codeType": "NOTICE","sortId": "2","name": "邮箱通知"}, {"code": "3","codeType": "NOTICE","sortId": "3","name": "微信消息通知"}],"ALRAM": [{"code": "1","codeType": "ALRAM","sortId": "1","name": "普通告警"}, {"code": "2","codeType": "ALRAM","sortId": "2","name": "中级告警"}, {"code": "3","codeType": "ALRAM","sortId": "3","name": "严重告警"}, {"code": "4","codeType": "ALRAM","sortId": "4","name": "特级告警"}]
}

这结果顺序发生了变化，那该如何处理，保持内容不变呢？

LinkedHashMap

 public static void main(String[] args){String data = "[{\"codeType\":\"ALRAM\",\"code\":\"1\",\"name\":\"普通告警\",\"sortId\":\"1\"},{\"codeType\":\"ALRAM\",\"code\":\"2\",\"name\":\"中级告警\",\"sortId\":\"2\"},{\"codeType\":\"ALRAM\",\"code\":\"3\",\"name\":\"严重告警\",\"sortId\":\"3\"},{\"codeType\":\"ALRAM\",\"code\":\"4\",\"name\":\"特级告警\",\"sortId\":\"4\"},{\"codeType\":\"NOTICE\",\"code\":\"1\",\"name\":\"短信通知\",\"sortId\":\"1\"},{\"codeType\":\"NOTICE\",\"code\":\"2\",\"name\":\"邮箱通知\",\"sortId\":\"2\"},{\"codeType\":\"NOTICE\",\"code\":\"3\",\"name\":\"微信消息通知\",\"sortId\":\"3\"}]";JSONArray items = JSON.parseArray(data);Map<String, ArrayList<JSONObject>> alram = ListUtils.emptyIfNull(items).stream().map(e -> (JSONObject) e).collect(Collectors.groupingBy(e -> MapUtils.getString(e, "codeType"),LinkedHashMap::new,Collectors.toCollection(ArrayList::new)));System.out.println(JSON.toJSONString(alram));}

结果：

{"ALRAM": [{"code": "1","codeType": "ALRAM","sortId": "1","name": "普通告警"}, {"code": "2","codeType": "ALRAM","sortId": "2","name": "中级告警"}, {"code": "3","codeType": "ALRAM","sortId": "3","name": "严重告警"}, {"code": "4","codeType": "ALRAM","sortId": "4","name": "特级告警"}],"NOTICE": [{"code": "1","codeType": "NOTICE","sortId": "1","name": "短信通知"}, {"code": "2","codeType": "NOTICE","sortId": "2","name": "邮箱通知"}, {"code": "3","codeType": "NOTICE","sortId": "3","name": "微信消息通知"}]
}