how to use java 8 stream and lambda to flatMap a groupingBy result

Question

I have a object with contains a list of other objects and I want to return a flatmap of the contained objects mapped by some property of the container. Any one if is it poss

Answer 1

You could try something like:

Map> res = operations.parallelStream().filter(s -> s.getTotal() > 10)
    .collect(groupingBy(Selling::getClientName, mapping(Selling::getProducts,
        Collector.of(ArrayList::new, List::addAll, (x, y) -> {
            x.addAll(y);
            return x;
        }))));