java-converting-optionals-list

Three approaches to Optionals list conversion (using streams).

prior java 9

• filter + map

  dataStream()
      .filter(Optional::isPresent)
      .map(Optional::get)
  

• flatMap

  dataStream()
      .flatMap(x -> x.map(Stream::of).orElseGet(Stream::empty))
  

java 9

• flatMap + Optional as a stream

  dataStream()
      .flatMap(Optional::stream)
  

Remark: Internally Optional::stream is implemented:

public Stream<T> stream() {
    if (!isPresent()) {
        return Stream.empty();
    } else {
        return Stream.of(value);
    }
}    

tests

Fully tested in OptionalListConversionTest.