import static java.util.stream.IntStream.range;
import static java.util.stream.IntStream.rangeClosed;

private List<String> possibleNgrams(String[] words) {
    return rangeClosed(1, words.length)
        .mapToObj(
            window ->
                rangeClosed(0, words.length - window)
                    .mapToObj(
                        i ->
                            range(i, i + window)
                                .mapToObj(x -> words[x])
                                .collect(Collectors.joining(" "))))
        .flatMap(Function.identity())
        .collect(Collectors.toList());
}

System.out.println(possibleNgrams("pale ale beer".split("\\s+"))

> ["pale ale beer", "pale ale", "ale beer", "pale", "ale", "beer"]