Java 8 / Lambda：多个collect / Collectors.groupingBy with sorted

Im having the following code

我有以下代码

    Map<BigDecimal, Map<Optional<BigDecimal>, List<TestDto>>> test =  data.getTestDtos().stream()
    .collect(
            Collectors.groupingBy(TestDto::getValue1,
            Collectors.groupingBy(dto -> Optional.ofNullable(dto.getValue2()))));
    Map