如何转换可选 <List<A> &gt;至可选 <List<B> &gt;

Question

Let's say I have a method:

B someMethod(A) {
    // ...
}

And I have an Optional<List<A>> , how can I convert it to Optional<List<B>> ?

Answer 1

Use Optional.map to change Optional of one thing to Optional of another:

import static java.util.stream.Collectors.toList;

Optional<List<B>> optListB = optListA.map(
        listOfA -> listOfA.stream()
                .map(SomeClass::someMethod)
                .collect(toList())
);

(assuming someMethod is a static method of SomeClass )