使用一系列依赖的future和non-future方法调用进行scala异常处理

我有一个方法可能会返回 Future - 成功或失败，甚至可以抛出异常 . 我可以通过在整个方法上放置try catch块并一直返回Future来避免这种情况，但我现在想避免它 . 调用这样的方法我几乎没有问题：

1）在调用者代码中，如果我使用 map ，我期望执行一个方法并期望一个Future或异常，我试图按以下方式处理：

object ETLCoordinator {      

  private def getBusinessListFromModules(modulePaths: Iterable[File]) : Future[String] = {
    implicit val ec = ExecutionContext.global
    println("Inside getBusinessListFromModules..")
    throw new java.lang.RuntimeException("failed to get businesses") //Exception is thrown before future was constructed
    Future("ok")
  }

  def main(args: Array[String]) {

    println("Inside Future Test..")
    implicit val ec = ExecutionContext.global
    val modulePaths = Iterable(new File("mdrqaint/MDR/QAINT/QAINTX"))

    val fut1 = getBusinessListFromModules(modulePaths) //This is outside of try and which should be okay
    try { 
      fut1.map { res =>
        println("things after Successful fut1")
      }.recover{
        case t: Throwable => println("Failed future in fut1: "+ t.getMessage)
      }  
    } catch {
      case t: Throwable => println("Exception in fut1: "+ t.getMessage)
    }
  }    
}

输出:(上面没有执行recover或catch块）

Inside Future Test..
Inside getBusinessListFromModules..
Exception in thread "main" java.lang.RuntimeException: failed to get businesses

但是如果我把 val fut1 = getBusinessListFromModules(modulePaths) 放在Try块中，那么Exception会被Catch块捕获并得到输出：

Inside Future Test..
Inside getBusinessListFromModules..
Exception in fut1: failed to get businesses

为什么是这样？我虽然在调用map，flatmap，onSuccess，onComplete等方法时会执行Future执行 . 在这种情况下，调用 map 已经在Try块中 .

2）定义和调用此类方法的更好方法是什么？在调用者中尝试/ catch块或者尝试/ catch方法本身？或任何其他方式 . 我尝试在Future中包装调用方法，所以我在调用者中得到Future [Future [String]] . 我能够避免所有尝试捕获 .

val fut1 = Future(getBusinessListFromModules(modulePaths))
//try {
  fut1.map { res =>
    res.map{ str =>
      println("things after Successful fut1")  
    }.recover{
      case t: Throwable => println("Failed in future of fut1: "+ t.getMessage)
    } 
    println("things after Successful fut1 wrapper")
  }.recover{
    case t: Throwable => println("Failed to create future in fut1: "+ t.getMessage)
  }

3）如果中间有另一种方法委托给 getBusinessListFromModules 但它本身就是非未来的方法 .

object ETLController {

  private def getBusinessListFromModules(modulePaths: Iterable[File]) : Future[String] = {
    implicit val ec = ExecutionContext.global
    println("Inside getBusinessListFromModules..")
    //throw new java.lang.RuntimeException("failed to get businesses")
    Future("ok")
  }

  private def callGetBusList(modulePaths: Iterable[File]) : String = {

    implicit val ec = ExecutionContext.global
    val etlF = getBusinessListFromModules(modulePaths)    

    etlF onComplete { 
      case Success(itr) => {
        println("Future getBusinessListFromModules success: "+ itr)
        throw new java.lang.RuntimeException("RTE from callGetBusList")
      }
      case Failure(t) => {
        println("Future getBusinessListFromModules throws an error")
      }
    }

    "callGetBusList was a success"
  }

  def main(args: Array[String]) {

    println("Inside Future Test..")
    implicit val ec = ExecutionContext.global
    val modulePaths = Iterable(new File("mdrqaint/MDR/QAINT/QAINTX"))
    try {
      val fut = Future(callGetBusList(modulePaths))
      fut.map { res =>
        println("successful future!")
      }.recover{
        case t: Throwable => println("Failed future: "+ t.getMessage)
      }
    } catch {
      case t: Throwable =>   println("callGetBusList failed:" + t.getMessage)
    }

  }    
}

输出:(没有恢复或捕获块执行！）

Inside Future Test..
Inside getBusinessListFromModules..
Future getBusinessListFromModules success: ok
java.lang.RuntimeException: RTE from callGetBusList
    at ..
successful future!

我甚至尝试双重包装Future调用：

val fut = Future(Future(callGetBusList(modulePaths)))
fut.map { res =>
  res.map { str =>
    println("successful inner future! "+ str)
  }.recover{
    case t: Throwable => println("Failed inner future: "+ t.getMessage)
  }
  println("successful outer future!")
}.recover{
  case t: Throwable => println("Failed outer future: "+ t.getMessage)
}

输出：

Future getBusinessListFromModules success: ok
java.lang.RuntimeException: RTE from callGetBusList
    at 
successful inner future! callGetBusList was a success
successful outer future!

我得到的"callGetBusList was a success"好像 RuntimeException 里面 onComplete 方法迷路了！如何在最终来电者中捕获它？处理此类未来依赖关系的更好做法是什么？

更新：基于@dk14解释，选择转换中间方法返回Future，基本上所有方法都返回某种Future而不是简单的Exception .

object ETLController {

  private def getBusinessListFromModules(modulePaths: Iterable[File]) : Future[String] = {
    implicit val ec = ExecutionContext.global
    println("Inside getBusinessListFromModules..")
    Future {
      Thread.sleep(2000)
      throw new java.lang.RuntimeException("failed to get businesses")
      "ok"
    }
  }

  private def callGetBusList(modulePaths: Iterable[File]) : Future[String] = {

    implicit val ec = ExecutionContext.global
    val etlF = getBusinessListFromModules(modulePaths)    

    etlF map { itr => 
        println("Future getBusinessListFromModules success: "+ itr)
        throw new java.lang.RuntimeException("RTE from callGetBusList")
      } recover {
      case t: Throwable => {
        println("Future callGetBusList throws an error: " + t.getMessage)
        throw t
      }
    }    
  }

  def main(args: Array[String]) {

    println("Inside Future Test..")
    implicit val ec = ExecutionContext.global
    val modulePaths = Iterable(new File("mdrqaint/MDR/QAINT/QAINTX"))
    val fut = callGetBusList(modulePaths)
    fut.map { str =>
        println("successful  future! "+ str)
    }.recover{
      case t: Throwable => println("Failed  future: "+ t.getMessage)
    }
    println("Active threads: " +Thread.activeCount())
    sys.allThreads().foreach(t => t.join())

  }    
}