Remove all entries where value is an empty Optional from map

Question

I want to remove all entries where value is an empty Optional from the map. It would seem that nothing complicated, but I am trying to find a better solution that I have.

---

Input:

I have the following Map:

Map<String, Function<String, Optional<String>>> attributesToCalculate = new HashMap<>();

Where key - just a String and value - reference to method which returns Optional < String >

---

Output:

As a result, I want to get

Map<String, String> calculatedAttributes

(excluding entries where value was an empty Optional)

---

Here is my solution

      return attributesToCalculate.entrySet()
        .stream()
        .map(entry -> Pair.of(entry.getKey(), entry.getValue().apply(someString)))
        .filter(entry -> entry.getValue().isPresent())
        .collect(Collectors.toMap(Map.Entry::getKey, entry -> entry.getValue().get()));

But I don't like the .filter part because then I have to invoke .get() on Optional in collect part.

Is there а better way (maybe without .get invocation) to solve this problem? Thanks.

Answer 1

Not a very pretty one, and similar to for-loop:

 return attributesToCalculate.entrySet().stream().collect(HashMap::new, (sink, entry) -> {

    entry.getValue().apply(someString).ifPresent(v -> sink.put(entry.getKey(), v));

}, Map::putAll);