Returning default list if the list is empty using java 8 Streams?

Question

Is there any way so that the below can be performed as one set of stream operations, instead of explicitly checking if recommendedProducts is empty then return default list else return the filtered list?

public List<Product> getRecommendedProducts() {
    List<Product> recommendedProducts 
        = this.newProducts
              .stream()
              .filter(isAvailable)
              .collect(Collectors.toList());

    if (recommendedProducts.isEmpty()) {
        return DEFAULT_PRODUCTS;
    }

    return recommededProducts;
}

@AndyTurner Agree. The code is good as it is. The only improvement I would do is using *ternary operator* instead of *if-else* statement. It is still a matter of taste though. — ETO, Oct 07 '19 at 20:53
@ETO There is nothing wrong, but I was trying/hoping to find out if there is a way to do it just by using Stream APIs with out explicit condition checks. Thanks for the reply - I like the ternary operator suggestion. — user3495691, Oct 07 '19 at 21:51

score 9 · Accepted Answer · answered Oct 07 '19 at 21:41

You can try this:

List<Product> recommendedProducts 
        = this.newProducts
              .stream()
              .filter(isAvailable)
              .collect(Collectors.collectingAndThen(Collectors.toList(), list -> list.isEmpty() ? DEFAULT_PRODUCTS : list));

score 5 · Answer 2 · edited Oct 08 '19 at 03:26

5

While you could achieve your goal using Optional, I would still opt for plain old ternary operator.

In this particular case it makes much more sense and improves readability:

return recommendedProducts.isEmpty() ? DEFAULT_PRODUCTS : recommendedProducts;

edited Oct 08 '19 at 03:26

Naman

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answered Oct 07 '19 at 20:50

ETO

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score 3 · Answer 3 · answered Oct 07 '19 at 20:31

Yes by using Optional

return Optional.of(this.newProducts.stream()
                                   .filter(isAvailable)
                                   .collect(Collectors.toList()))
                    .filter(l->!l.isEmpty())
                    .orElse(DEFAULT_PRODUCTS);

Returning default list if the list is empty using java 8 Streams?

3 Answers3