如何在Java 8中实现Elvis运算符? [英] How to implement the Elvis operator in Java 8?

问题描述

我有一个经典的猫王运算符"案例，我在其中调用每个可能返回null并将它们链接在一起的方法:

I have the classic "Elvis operator" case, where I'm calling methods that each may return null and chaining them together:

thing?:nullableMethod1(a)?:nullableMethod2(b)?:nullableMethod3()

在Java 8中，我发现的最可靠的实现是这样的:

In Java 8, the most faithful implementation I've found is something like this:

return Optional.ofNullable(thing)
    .flatMap(x -> Optional.ofNullable(x.nullableMethod1(a)))
    .flatMap(y -> Optional.ofNullable(y.nullableMethod2(b)))
    .flatMap(z -> Optional.ofNullable(z.nullableMethod3()))

我希望Java的Optional与elvis运算符类似:

I wish that Java's Optional had something akin to the elvis operator:

public<U> Optional<U> elvisOperator(Function<? super T, ? extends U> mapper) {
    return flatMap(t -> Optional.ofNullable(mapper.apply(t));
}

这样我就不必包装每个返回值:

So that I wouldn't have to wrap each return value:

return Optional.ofNullable(thing)
    .elvisOperator(x -> x.nullableMethod1(a))
    .elvisOperator(y -> y.nullableMethod2(b))
    .elvisOperator(Z::nullableMethod3); // also nice

在Java 8中是否有更高效，更惯用的方式实现Elvis运算符模式?

Is there a more efficient and idiomatic way to implement the Elvis operator pattern in Java 8?

推荐答案

也许我正在忽略某些内容，但是是否有不能使用Optional#map的原因呢?

Maybe I'm overlooking something, but is there a reason that you can't use Optional#map?

以下示例不打印任何内容，因为Optional是短路，也就是说，如果Optional内部的值不存在(它是null或为空)，将其视为空.

The following example prints nothing, as Optional is short-circuiting in the sense that, if the value inside the Optional doesn't exist (it's null or the Optional is empty), it's treated as empty.

Optional.ofNullable("test")
        .map(s -> null)
        .ifPresent(System.out::println);

基于这个原因，我认为您可以执行以下操作:

For that reason, I'd think you could just do the following:

return Optional.ofNullable(thing)
               .map(x -> x.nullableMethod1(a))
               .map(y -> y.nullableMethod2(b))
               .map(Z::nullableMethod3);

这将映射您的thing(如果存在)，否则返回一个空的Optional.

This would map your thing if it exists, or return an empty Optional otherwise.

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