How to Replace Many if Statements in Java 에서 3.4. Rule Engine 적용버전

Policy.java

/**
 * How to Replace Many if Statements in Java(https://www.baeldung.com/java-replace-if-statements)
 * - 3.4. Rule Engine 적용버전
 */
public interface Policy<T, R> {

    boolean evaluate(T t, PolicyConditions policyConditions);

    R apply(T t, PolicyConditions policyConditions);
}

PriceInfoPolicy.java

public class SomePolicy implements Policy<SomePolicyHelper, SomeResult> {
    @Override
    public boolean evaluate(SomePolicyHelper somePolicyHelper, PolicyConditions policyConditions) {
        // return 해당 정책 적용여부
    }

    @Override
    public SomeResult apply(SomePolicyHelper somePolicyHelper, PolicyConditions policyConditions) {
        // return 정책 반영 결과
    }
}

PriceInfoProvider.java

public class PriceInfoProvider {

    private final List<Policy> policies;

    public SomeResult provide(SomePolicyHelper somePolicyHelper, PolicyConditions policyConditions) {
        PriceInfoPolicy priceInfoPolicy = policies
            .stream()
            .filter(policy -> policy.evaluate(somePolicyHelper, policyConditions))
            .findFirst()
            .orElseThrow(() -> new RuntimeException(EXCEPTION_MESSAGE));
        return priceInfoPolicy.apply(somePolicyHelper, policyConditions);
    }
}