suggestedPostsForAsync.java

public Iterable<PostSummary> suggestedPostsFor(ProfileId profileId) {
    try {
        Future<Iterable<ProfileId>> friendIds = friendsOf(profileId);
        Set<Topic> topics = favoriteTopicsOf(profileId).get();
        Stream<PostSummary> interestingPosts = stream(friendIds.get())
                .parallel() // Stream parallelization
                .flatMap(friendId -> lastPostsOf(friendId))
                .filter(post -> post.isAbout(topics));
        return mostLiked(3, interestingPosts);
    } catch (Exception e) { // InterruptedException and ExecutionException
        // Raise high level abstract error?
    }
}