scala 模式匹配以检查字符串是否为空或空
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/27941585/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Pattern Matching to check if string is null or empty
提问by placplacboom
Is it possible to check if string is null or empty using match?
是否可以使用匹配来检查字符串是否为空或为空？
I'm trying to do something like:
我正在尝试执行以下操作：
def sendToYahoo(message:Email) ={
val clientConfiguration = new ClientService().getClientConfiguration()
val messageId : Seq[Char] = message.identifier
messageId match {
case messageId.isEmpty => validate()
case !messageId.isEmpty => //blabla
}
}
But i have a compile error.
但是我有一个编译错误。
Thank in advance.
预先感谢。
回答by Gabriele Petronella
You can write a simple function like:
您可以编写一个简单的函数，例如：
def isEmpty(x: String) = Option(x).forall(_.isEmpty)
or
或者
def isEmpty(x: String) = x == null || x.isEmpty
You might also want to trim the string, if you consider " "to be empty as well.
如果您也认为" "是空的，您可能还想修剪字符串。
def isEmpty(x: String) = x == null || x.trim.isEmpty
and then use it
然后使用它
val messageId = message.identifier
messageId match {
case id if isEmpty(id) => validate()
case id => // blabla
}
or without a match
或没有 match
if (isEmpty(messageId)) {
validate()
} else {
// blabla
}
or even
甚至
object EmptyString {
def unapply(s: String): Option[String] =
if (s == null || s.trim.isEmpty) Some(s) else None
}
message.identifier match {
case EmptyString(s) => validate()
case _ => // blabla
}
回答by Lee
def isNullOrEmpty[T](s: Seq[T]) = s match {
case null => true
case Seq() => true
case _ => false
}
回答by Kamau
If you're looking to check whether a String is null or empty, here's a one-liner that does that. You wrap it with an Option, use filter to make sure it's not an empty String then call getOrElse to provide a default value in case the original value is either null or an empty String.
如果您想检查 String 是 null 还是空，这里有一个单行程序可以做到这一点。你用一个选项包装它，使用过滤器来确保它不是一个空字符串，然后调用 getOrElse 来提供一个默认值，以防原始值为空或空字符串。
Option(s).filter(!_.isEmpty).getOrElse(columnName)
