Java 8可选:ifPresent返回对象或ElseThrow异常 [英] Java 8 optional: ifPresent return object orElseThrow exception

问题描述

我正在尝试做这样的事情:

I'm trying to make something like this:

 private String getStringIfObjectIsPresent(Optional<Object> object){
        object.ifPresent(() ->{
            String result = "result";
            //some logic with result and return it
            return result;
        }).orElseThrow(MyCustomException::new);
    }

这将不起作用，因为ifPresent将消费者功能接口作为参数，其具有无效的accept(T t).它不能返回任何值.还有其他方法吗?

This won't work, because ifPresent takes Consumer functional interface as parameter, which has void accept(T t). It cannot return any value. Is there any other way to do it ?

推荐答案

实际上，您要搜索的是:

Actually what you are searching is: Optional.map. Your code would then look like:

object.map(o -> "result" /* or your function */)
      .orElseThrow(MyCustomException::new);

如果可以的话，我宁愿忽略传递Optional.最后，您在这里使用Optional一无所获.另一种变体:

I would rather omit passing the Optional if you can. In the end you gain nothing using an Optional here. A slightly other variant:

public String getString(Object yourObject) {
  if (Objects.isNull(yourObject)) { // or use requireNonNull instead if NullPointerException suffices
     throw new MyCustomException();
  }
  String result = ...
  // your string mapping function
  return result;
}

如果由于另一个调用而已经具有Optional对象，出于单个原因，我仍然建议您使用map方法而不是isPresent等，因为我发现它更多可读(显然是主观决定；-)).

If you already have the Optional-object due to another call, I would still recommend you to use the map-method, instead of isPresent, etc. for the single reason, that I find it more readable (clearly a subjective decision ;-)).

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