Remove all Optional empty/null values from arraylist in java

Question

I need to remove all empty/null values from List<Optional<String>>.

Example:

List<Optional<String>> list = new ArrayList<>();

list.add(Optional.empty());
list.add(Optional.of("Str1"));
list.add(Optional.of("Str2"));
list.add(Optional.of("Str3"));
list.add(Optional.of("Str4"));
list.add(Optional.of("Str5"));
list.add(Optional.empty());
list.add(Optional.ofNullable(null));

---

Currently, I'm using one of the below approaches:

Way 1:

List<String> collect = list.stream()
                   .filter(Optional::isPresent)
                   .map(obj ->obj.get())
                   .collect(Collectors.toList());

Way 2:

List<Optional<String>> emptlist = new ArrayList<>();
emptlist.add(Optional.empty());
list.removeAll(emptlist);

Is there any other better way?

Answer 1

With Java9, you can do this using the newly added Optional::stream API :

List<String> collect = list.stream()
               .flatMap(Optional::stream)
               .collect(Collectors.toList());

This method can be used to transform a Stream of optional elements to a Stream of present value elements.

Sticking with Java8, the Way1 in the question is good enough IMHO -

List<String> collect = list.stream()
               .filter(Optional::isPresent)
               .map(Optional::get) // just a small update of using reference
               .collect(Collectors.toList());