Refactoring nested for loop into Java 8 stream

Question

I have the following for loop:

    List<Map> mapList = new ArrayList<>();
    for (Resource resource : getResources()) {
        for (Method method : resource.getMethods()) {
            mapList.add(getMap(resource,method));
        }
    }
    return mapList;

How could I refactor this nested loop into a Java 8 stream?

Answer 1

You can use flatMap to obtain all the Maps for all Methods of all Resources :

List<Map> mapList = 
    getResources().stream()
                  .flatMap(r->r.getMethods().stream().map(m->getMap(r,m)))
                  .collect(Collectors.toList());