[FIXED] Java Sorting with Optional List which maybe null

Issue

How do I do sorting with an Optional? The following is not working. mainProducts or productSublist maybe null. We are returning productSubList sorted by Date .

List<ProductSubList> productSubList = Optional.of(mainProducts)
        .map(MainProducts::getProductSubList)
        .ifPresent(list -> list.stream().sorted(Comparator.comparing(ProductSubList::getProductDate))
        .collect(Collectors.toList()));

Error:

Required type: ProductSubList ; Provided:void

Part Answer which seems too long, is there a way to make this shorter?

  if (Optional.of(mainProducts).map(MainProducts::getProductSubList).isPresent()) {
      productSublist = mainProducts.getProductSubList().stream()
              .sorted(Comparator.comparing(ProductSubList::getProductDate))
              .collect(Collectors.toList());
    }

Resource: How to avoid checking for null values in method chaining?

Solution

Seems you're looking for something like this:

List<ProductSubList> productSubList = Optional.ofNullable(mainProducts)
        .map(MainProducts::getProductSubList)
        .map(list -> list.stream()
                .sorted(Comparator.comparing(ProductSubList::getProductDate))
                .collect(Collectors.toList()))
        .orElse(Collections.emptyList());

Answered By - shmosel
Answer Checked By - Timothy Miller (JavaFixing Admin)