Groovy是否具有专用语法来查找集合中的元素或抛出异常(如果找不到)

Question

当前在Groovy中，我需要编写以下内容以实现简单逻辑：

def sampleList = [1, 2]
def element = sampleList.find { it == 3 }
if (!element) {
    throw new IllegalStateException('Element not found!')
}

使用Java流，这只是更简单：

def sampleList = [1, 2]
sampleList.stream().filter { it == 3 }.findFirst().orElseThrow {
    new IllegalStateException('Element not found!')
}

是否还有其他简洁的Groovy语法可以执行相同的任务？

Answer 1

选项1 我认为这是最清晰的，利用Optional API：

def sampleList = [1, 2]
def element = Optional.ofNullable(sampleList.find{it==3}).orElseThrow{new IllegalStateException('Element not found!')}

选项2

我不认为这很棒，但是您可以从封闭中调用throw，并使用猫王?:操作员

def sampleList = [1, 2]
def element = sampleList.find{it==3} ?: {throw new IllegalStateException('Element not found!')}()
//Alternately: ...{throw new IllegalStateException('Element not found!')}.call() to make it more readable

投掷：

Exception thrown
java.lang.IllegalStateException: Element not found!
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at ConsoleScript20$_run_closure2.doCall(ConsoleScript20:2)
    at ConsoleScript20$_run_closure2.doCall(ConsoleScript20)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at ConsoleScript20.run(ConsoleScript20:2)
    at jdk.internal.reflect.GeneratedMethodAccessor218.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

在Groovy Console中

选项3 另一个选项是将所有逻辑提取到指定的关闭中：

def sampleList = [1, 2]
def tester = {list, value -> if(value in list){value} else{throw new IllegalStateException('Element not found!')}}
tester(sampleList, 3)