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

user_3495691 0
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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;
}
java-stream java-8 option-type collections java
3 Answers

You can try this:

List<Product> recommendedProducts 
        = this.newProducts
              .stream()
              .filter(isAvailable)
              .collect(Collectors.collectingAndThen(Collectors.toList(), list -> list.isEmpty() ? DEFAULT_PRODUCTS : list));
user_16788930

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;
user_105846050

Yes by using Optional

return Optional.of(this.newProducts.stream()
                                   .filter(isAvailable)
                                   .collect(Collectors.toList()))
                    .filter(l->!l.isEmpty())
                    .orElse(DEFAULT_PRODUCTS);
user_99591520
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