Scala 恢复或recoverWith

我们公司正在用Scala开发一些系统，我们有一些疑问。我们正在讨论如何映射未来的异常，但我们不知道何时应该使用选项 1 或选项 2。

val created: Future[...] = ???

选项1：

val a = created recover {   
  case e: database.ADBException =>
    logger.error("Failed ...", e)
    throw new business.ABusinessException("Failed ...", e) 
}

选项2：

val a = created recoverWith {   
  case e: database.ADBException =>
    logger.error("Failed ...", e)
    Future.failed(new business.ABusinessException("Failed ...", e))
}

有人可以解释一下我什么时候应该选择选项1或选项2吗？有什么区别？

嗯，答案在 scaladocs 中有清楚的描述：

  /** Creates a new future that will handle any matching throwable that this
   *  future might contain. If there is no match, or if this future contains
   *  a valid result then the new future will contain the same.
   *
   *  Example:
   *
   *  {{{
   *  Future (6 / 0) recover { case e: ArithmeticException => 0 } // result: 0
   *  Future (6 / 0) recover { case e: NotFoundException   => 0 } // result: exception
   *  Future (6 / 2) recover { case e: ArithmeticException => 0 } // result: 3
   *  }}}
   */
  def recover[U >: T](pf: PartialFunction[Throwable, U])(implicit executor: ExecutionContext): Future[U] = {

  /** Creates a new future that will handle any matching throwable that this
   *  future might contain by assigning it a value of another future.
   *
   *  If there is no match, or if this future contains
   *  a valid result then the new future will contain the same result.
   *
   *  Example:
   *
   *  {{{
   *  val f = Future { Int.MaxValue }
   *  Future (6 / 0) recoverWith { case e: ArithmeticException => f } // result: Int.MaxValue
   *  }}}
   */
  def recoverWith[U >: T](pf: PartialFunction[Throwable, Future[U]])(implicit executor: ExecutionContext): Future[U] = {

recover将普通结果包装在Future为你（类似map）， 尽管recoverWith期望Future结果（模拟flatMap).

所以，这是经验法则：

如果你恢复了已经返回的东西Future, use recoverWith，否则使用recover.

update在你的情况下，使用recover是首选，因为它将异常包装在Future为你。否则不会有任何性能提升或任何东西，所以你只是避免一些样板。