Collectors. Groupingby sort

background

Recently, project development used to group collections , After grouping according to the area, it is found that the order is inconsistent with the set

Find the problem

The data set found

Use after sorting groupingBy Aggregate , It is found that the order of data has changed

The exploration process

Open source
The first parameter ： Group by which field

The second parameter ： What container does the group use to save and return

The third parameter ： How to collect the results after grouping

The problem should be the second parameter The default with hashmap Save the grouped data hashmap disorder

Problem solving

Replace the second parameter with LinkedHashMap