Java 8: Stream and filter based on optional conditions - java-8

Question

Example: Filter a list of products that have a price based on fromPrice and toPrice. They could either both be supplied, or just one.
Find all products whose price is greater than fromPrice
Find all products whose price is less than toPrice
Find all products whose price is between fromPrice and toPrice
Product:
public class Product {
private String id;
private Optional<BigDecimal> price;
public Product(String id, BigDecimal price) {
this.id = id;
this.price = Optional.ofNullable(price);
}
}
PricePredicate:
public class PricePredicate {
public static Predicate<? super Product> isBetween(BigDecimal fromPrice, BigDecimal toPrice) {
if (fromPrice != null && toPrice != null) {
return product -> product.getPrice().isPresent() && product.getPrice().get().compareTo(fromPrice) >= 0 &&
product.getPrice().get().compareTo(toPrice) <= 0;
}
if (fromPrice != null) {
return product -> product.getPrice().isPresent() && product.getPrice().get().compareTo(fromPrice) >= 0;
}
if (toPrice != null) {
return product -> product.getPrice().isPresent() && product.getPrice().get().compareTo(toPrice) <= 0;
}
return null;
}
}
Filters:
return this.products.stream().filter(PricePredicate.isBetween(fromPrice, null)).collect(Collectors.toList());
return this.products.stream().filter(PricePredicate.isBetween(null, toPrice)).collect(Collectors.toList());
return this.products.stream().filter(PricePredicate.isBetween(fromPrice, toPrice)).collect(Collectors.toList());
Is there a way to improve my Predicate instead of having the if not null checks? Anything that can be done with optionals?

Answer 1

No, Optional is not designed to replace null checks.
But your code can be improved by avoiding duplication, and by avoiding to return null (which is clearly not a valid value for a Predicate) if both arguments are null:
public static Predicate<Product> isBetween(BigDecimal fromPrice, BigDecimal toPrice) {
Predicate<Product> result = product -> true;
if (fromPrice != null) {
result = result.and(product -> product.getPrice().isPresent() && product.getPrice().get().compareTo(fromPrice) >= 0);
}
if (toPrice != null) {
result = result.and(product -> product.getPrice().isPresent() && product.getPrice().get().compareTo(toPrice) <= 0);
}
return result;
}

Answer 2

You can use Apache Commons Lang, it offers null safe comparison:
ObjectUtils.compare(from, to)
null is assumed to be less than a non-value