collectors排序,Collectors.groupingBy（）返回按升序排序的结果java

I am sending result in descending order but I get output with ascending order

List myData = new ArrayList<>();

Map> myid = new LinkedHashMap<>();

try {

myData = myService.getData(id);

myid = myData.stream().collect(Collectors.groupingBy(myEntity::getDataId));

Here mydata is sorted by desc order but after creating collections by group data id my list get sorted with ascending order. I want my collection list to be descending order not ascending order.

解决方案

As @Holger described in Java 8 is not maintaining the order while grouping

, Collectors.groupingBy() returns a HashMap, which does not guarantee order.

Here is what you can do:

myid = myData.stream()

.collect(Collectors.groupingBy(MyEntity::getDataId,LinkedHashMap::new, toList()));

Would return a LinkedHashMap>. The order will also be maintained as the list used by collector is ArrayList.