How to use Java stream to collect multiple lists into one list?

There is already an answer to this question: > java8 lambda: concat LIST1

List<MyListService> services;

services.stream().XXX.collect(Collectors.toList());


interface MyListService {
   List<MyObject> getObjects();
}

Because I completely control the interface: or should I change the method to return an array instead of a list?

Solution

You can use flatmap to collect the lists contained in the mylistservice instance:

List<MyObject> list = services.stream()
                              .flatMap(s -> s.getObjects().stream())
                              .collect(Collectors.toList());