Java8 Lambda: concat list

Question

I am trying to concat list of a stream and process it.

class A {
    public List<B> bList;
}
List<A> aList;
aList.stream().map(a -> a.bList)....

Here i get several list of b.

But, I would like to collect all my b in only one list. Any ideas ?

Answer 1

That's what flatMap is for :

List<B> bList = aList.stream()
                     .flatMap(a -> a.bList.stream())
                     .collect(Collectors.toList());