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.
As commented above, there is nothing wrong with using get if you have already checked that the Optional is not empty.
However, I think this code is best expressed without using streams.
Map<String, String> result = new HashMap<>();
attributesToCalculate.forEach((k, v) ->
v.apply(someString).ifPresent(str -> result.put(k, str))
);
If you don't like using forEach to populate the map in that way, you can use a simple for loop instead.