Map sorts according to the key value (ascending plus descending)

Map according to Key Value to sort

If this article helps you , I hope I can praise the blogger , thank ！！

When writing a function today , You need to group by date , So when I look it up from the database, I use order by create_time desc Sort in descending order , At first, the data is sorted normally , But when I use stream() After grouping , It is found that there is a problem in data sorting

Group by date first , Date as Map Of key, The data list corresponding to the date is used as value For storage , But it can be seen from the figure that this date is not in descending order , This will cause the front end to obtain these data and cannot output them in the correct order .
So we have to deal with this listMap Sort again .

List<EarnDetailParam> list=cereShopOrderDAO.getEarnDetails(param);
list.stream().forEach(l->l.setDate(l.getCreateTime().split(" ")[0]));
Map<String,List<EarnDetailParam>> listMap = list.stream().collect(Collectors.groupingBy(EarnDetailParam::getDate));
Map<String, List<EarnDetailParam>> result = new LinkedHashMap<>();
listMap.entrySet().stream().sorted(Collections.reverseOrder(Map.Entry.comparingByKey())).forEachOrdered(x -> result.put(x.getKey(), x.getValue()));

First, we get data from the database according to the first statement , because create_time With time , So when grouping, you need a new variable to save create_time Date after cutting
list.stream().collect(Collectors.groupingBy(EarnDetailParam::getDate)) This statement uses the just obtained date Group operation , Then you will get the above figure .
Because the order is not the descending order we want , So we need to do the next step , Define a LinkedHashMap For storage , And then according to Map Of Key Sort , Because we want to operate in descending order , So we need to .sorted(Collections.reverseOrder(Map.Entry.comparingByKey())) Use reverseOrder In reverse order , Then assign the key value pair to result

.sorted(Map.Entry.comparingByKey()) It's in ascending order
.sorted(Collections.reverseOrder(Map.Entry.comparingByKey())) It's in reverse order

At this point, we will get the descending grouping we need , We have achieved the desired effect .