Refactoring Java 8 stream code - duplication of code

Question

I have two methods which are nearly the same:

public String find(Query query) {
        return PRODUCT.stream()
                .filter(byName(query.getName()))
                .filter(byCount(query.getNumber()))
                .map(getValueOf(query.getName()))
                .findFirst()
                .orElseThrow(() -> new IllegalArgumentException());
    }

and second:

public String findSpecial(Query query) {
        return SPECIAL_PRODUCTS.stream()
                .filter(byName(query.getName()))
                .filter(byCount(query.getNumber()))
                .filter(byIsDoubled(query.isDoubled()))
                .map(getValueOf(query.getName()))
                .findFirst()
                .orElseThrow(() -> new IllegalArgumentException());
    }

so the difference is only line .filter(byIsDoubled(query.isDoubled())).

Is there a good way to not duplicate methods body?

@YCF_L But I am duplicating 5 lines and only adding filter. It doesn't looks good for me — Michu93
– Michu93, Commented Oct 20, 2020 at 9:15
You can design something like filter(!isSpecial || byIsDoubled(query.isDoubled())) which return true if isSpecial is false and pass like find(Query query, boolean isSpecial) though I agree with @YCF_L and sometimes clean code is better than making complex to remove duplicate lines. — Eklavya
– Eklavya, Commented Oct 20, 2020 at 9:26
Do like this: public String find(Query query, List<Product> list,List<Predicate<Product>> predicates){ return list.stream().filter(product -> predicates.stream() .allMatch(productPredicate -> productPredicate.test(product))) .map(getValueOf(query.getName())) .findFirst() .orElseThrow(IllformedLocaleException::new); } — Hadi
– Hadi, Commented Oct 20, 2020 at 10:18

Shekhar Khairnar · Accepted Answer · 2020-10-20 11:19:02Z

1

You can do something like:

SPECIAL_PRODUCTS.stream().filter(findConditional(query)).map(getValueOf(query.getName()))
                    .findFirst()
                    .orElseThrow(() -> new IllegalArgumentException());



public static Predicate<String> findConditional(Query query) {
        List<Predicate<String>> l = new ArrayList<>();
        Predicate<String> defaultPredicate = s -> true;
        l.add(byName(query.getName()));
        l.add(byCount(query.getNumber()));
        if (query.isDoubled()) {
            l.add(byIsDoubled(query.isDoubled()));
        }
        return l.stream().reduce(defaultPredicate, (predicate1, predicate2) -> predicate1.and(predicate2));
    }

answered Oct 20, 2020 at 11:19

Shekhar Khairnar

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