Java stream: Grouping HashMap key values to prevent duplicate keys

Question

I have the following HashMap in my Java app:

final Map<UUID, Boolean> map = demoRepo.demoService.stream()
        .collect(Collectors.toMap(
                ProductDTO::getMenuUuid,
                ProductDTO::getStatus));

However, as the result contains multiple menuUuid value, I need to group them as the key does not contain the same value. So, how should I do this using stream?

Update: I also tried groupingBy as shown below, but I think the usage is not correct:

final Map<UUID, Boolean> map = sdemoRepo.demoService.stream()
                .collect(Collectors.groupingBy(
                        ProductDTO::getMenuUuid, LinkedHashMap::new,
                        Collectors.mapping(ProductDTO::getStatus)));

Suppose that I have the following stream:

MenuUuid   |   Status |
-----------------------
1              true
2              false
1              true
1              true
3              true
2              false

Then I need a map result like; 1:true, 2:false, 3:true

Answer 1

If all the user ids have the same boolean then just do the following:

final Map<UUID, Boolean> map = demoRepo.demoService.stream()
        .collect(Collectors.toMap(
                ProductDTO::getMenuUuid,
                ProductDTO::getStatus,
                (existingValue, newValue)->existingValue));

the last lambda, is a merge function. it is used to make a decision on how to merge duplicate keys. In this case, it just keeps the first that's already there. You could also use the new one since you aren't really altering the boolean and they are all the same value.

If your ProductDTO class uses UUID to determine equality via equals() you could also do the following:

final Map<UUID, Boolean> map = demoRepo.demoService.stream()
        .distinct()
        .collect(Collectors.toMap(
                ProductDTO::getMenuUuid,
                ProductDTO::getStatus));

This works because you won't have any duplicate UUID's