java8 listmap聚合后内容顺序不变

   学习了groupingBy的用法，在处理List

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> 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> 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"
	}]
}

总结：

        对于List