You can use Comparator.reverseOrder() to have a comparator giving the reverse of the natural ordering.
If you want to reverse the ordering of an existing comparator, you can use Comparator.reversed().
Sample code:
Stream.of(1, 4, 2, 5)
.sorted(Comparator.reverseOrder());
// stream is now [5, 4, 2, 1]
Stream.of("foo", "test", "a")
.sorted(Comparator.comparingInt(String::length).reversed());
// stream is now [test, foo, a], sorted by descending length