我应该在什么时候对Java中的映射元素进行排序？[关闭]

Question

User Role | Permission Uuid    
----------|----------------                     
0         | a465433f... 
0         | 43db5a33...
1         | 610e9040... 
0         | 94e85bef... 
1         | 34e85f32...

public class PermissionRequest {
    private UserRole userRole;
    private List<UUID> permissionUuidList;
}

Map<Integer, List<UUID>> userRolePermissionMap = new HashMap<>();
userRolePermissionMap.put(Integer.parseInt(cellList.get(USER_ROLE)),
    Collections.singletonList(UUID.fromString(cellList.get(PERMISSON_UUID))));

Answer 1

Map<Integer, List<UUID>> userRolePermissionMap =
        rowsList.stream() // Stream<Row> 
                .collect(Collectors.groupingBy(
                    cellList -> Integer.parseInt(cellList.get(USER_ROLE)),
                    TreeMap::new, // supplier of sorted map
                    Collectors.mapping(
                        cellList -> UUID.fromString(cellList.get(PERMISSON_UUID)),
                        Collectors.toList())
                ));

Map<Integer, List<UUID>> userRolePermissionMap = new TreeMap<>();

for (List<Cell> cellList : rowList) {
    userRolePermissionMap.computeIfAbsent(
        Integer.parseInt(cellList.get(USER_ROLE)),
        k -> new ArrayList<UUID>()
    )  // mutable List<UUID> is returned
    .add(UUID.fromString(cellList.get(PERMISSON_UUID)));
}