Java 8 Version - of Map of Lists with Condition

Question

I want to know how to check and retrieve the elements of a List inside a Map .

private Map<User, List<Offer>> shops = new ConcurrentHashMap<>(32);

//how to write this?
public List<Offer> getOffersOlderThan(int seconds){
    return this.shops.values().stream().forEach(
                x->x.stream()
                    .filter(y-> MyTime.currentTime.minusSeconds(seconds)
                                      .isBefore(y.getOfferBegin()))
}

I already tried to use a filter instead the first forEach but that didn't work either.

I want to retrieve the List of all Offer ´s which have an Timestamp before currentTime - seconds .

How do I return with Java 8 an Generic List? eg:

public List<Offer> getOffersByUser(User u){
    return this.shops.entrySet().stream().filter(x->x.getKey().getId()==u.getId())
               .collect(List::new) //how to parameterize?
}

Answer 1

For all Offers, use flatMap() and collect()

return shops.values().stream()
    .flapMap(List::stream)
    .filter(y-> MyTime.currentTime.minusSeconds(seconds).isBefore(y.getOfferBegin())
    .collect(Collectors.toList());

For only the user's offers:

return shops.getOrDefault(user, Collections.emptyList())
    .filter(y-> MyTime.currentTime.minusSeconds(seconds).isBefore(y.getOfferBegin())
    .collect(Collectors.toList());