Java8 Lambda 和异常 [英] Java8 Lambdas and Exceptions

问题描述

我想知道是否有人可以向我解释以下奇怪之处.我使用的是 Java 8 更新 11.

I wonder if someone could explain the following weirdness to me. I'm using Java 8 update 11.

给定这个方法

private <F,T> T runFun(Function<Optional<F>, T> fun, Optional<F> opt) {
   return fun.apply(opt) ;
}

如果我首先构造一个函数对象，并将它传递给上面的方法，事情就会编译.

If I first construct a function Object, and pass that in to the method above, things compile.

private void doesCompile() {
    Function<Optional<String>, String> fun = o -> o.orElseThrow(() -> new RuntimeException("nah"));
    runFun(fun, Optional.of("foo"));

}

但是，如果我将函数内联为 lambda，编译器会说

But, if I inline the function as a lambda, the compiler says

未报告的异常 X；必须被捕获或声明被抛出

unreported exception X; must be caught or declared to be thrown

private void doesNotCompile () {
    runFun(o -> o.orElseThrow(() -> new RuntimeException("nah")), Optional.of("foo"));
}

<小时>

更新:原来错误消息是由 maven 缩写的.如果直接用javac编译，则报错:

---

Update: Turns out the error message was abbreviated by maven. If compiled directly with javac, the error is:

error: unreported exception X; must be caught or declared to be thrown
            runFun(o -> o.orElseThrow(() -> new RuntimeException("nah")), Optional.of("foo"));
                                     ^
  where X,T are type-variables:
    X extends Throwable declared in method <X>orElseThrow(Supplier<? extends X>)
    T extends Object declared in class Optional

另请参阅此处，了解可运行的测试代码.

Also see here for runnable test code.

推荐答案

这就是为我解决问题的方法:

This is what solved the problem for me:

代替写作

optional.map(this::mappingFunction).orElseThrow(() -> new BadRequestException("bla bla"));

我写道:

optional.map(this::mappingFunction).<BadRequestException>orElseThrow(() -> new BadRequestException("bla bla"));

添加显式 有助于解决这些 lambda 边缘情况(这很烦人...)

Adding the explicit <BadRequestException> helps with these lambda edge cases (which are quite annoying...)

更新:这是为了防止您无法更新到最新的 JDK 版本，如果可以，您应该...

UPDATE: This is in case you can't update to the latest JDK version, if you can you should...

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