级联方法，每个方法返回一个Java8可选[duplicate]

Question

import java.util.Optional;

public class OptionalCascade {

    public static void main(String[] args) {
        Optional<String> result = 

                // try to get a result with method A
                methodA()

                // if method A did not return anything, then try method B
                .orElseFlatMap(methodB());
    }


    static Optional<String> methodA() {
        return Optional.empty();
    }

    static Optional<String> methodB() {
        return Optional.empty();
    }
}

Answer 1

Optional<String> result = Optional.ofNullable(methodA().orElseGet(
        () -> methodB().orElse(null)));

public static <T> Optional<T> orElseFlatMap(Optional<T> optional,
        Supplier<Optional<T>> other) {
    return optional.isPresent() ? optional : other.get();
}

Optional<String> result = orElseFlatMap(methodA(), () -> methodB());