如何以功能方式验证参数？

Question

我正在编写Scala/Play 2.0应用程序,我希望我的代码根据请求返回不同的页面.这是我的代码:

// Validate client and return temporary credentials
def requestToken = Action { request =>
  // Authorization header may present or not
  val authHeader = parseHeaders(request headers AUTHORIZATION)
  // Authorization header may contain such keys or not
  val clientKey = authHeader("oauth_consumer_key")
  val signature = authHeader("oauth_signature")

  if (authenticateClient(clientKey, signature)) {
    ...
    Ok(...)
  } else {
    Unauthorized(...)
  }

}

当请求格式错误且某些标头丢失时,会出现问题,然后抛出NoSuchElementException.

在命令式语言中,我会验证这样的每一步:

if (!request.headers.contains(AUTHORIZATION))
  return Unathorized

val authHeader = parseHeaders(request headers AUTHORIZATION)

if (!authHeader.contains("oauth_consumer_key") || !authHeader.contains("oauth_signature"))
  return Unathorized

val clientKey = authHeader("oauth_consumer_key")
val signature = authHeader("oauth_signature")

...

但是我该怎样做才能以功能的方式解决这个问题？

Answer 1

您可以使用authHeader.get(key)哪个返回选项[B].您的代码看起来像这样:

val result = for {
  auth <- request.headers.get(AUTHORIZATION)
  authHeader = parseHeaders(auth)
  clientKey <- authHeader.get("oauth_consumer_key")
  signature <- authHeader.get("oauth_signature")
} yield { ... }

result.getOrElse(Unauthorized)

说明:

如果没有None值,则只执行整个表达式.因此,如果所有标题都存在,您将获得一个result,Some[A]如果一个或多个不存在,您将获得None.result.getOrElse(Unauthorized)将返回for Some[A]和Unauthorizedfor 的包含值None.