Try Some None

HadoopRDD.scala

  override def getPreferredLocations(split: Partition): Seq[String] = {
    val locs: Option[Seq[String]] = HadoopRDD.SPLIT_INFO_REFLECTIONS match {
      case Some(c) =>
        try {
          val lsplit = c.inputSplitWithLocationInfo.cast(hsplit)
          val infos = c.getLocationInfo.invoke(lsplit).asInstanceOf[Array[AnyRef]]
          Some(HadoopRDD.convertSplitLocationInfo(infos))
        } catch {
          case e: Exception =>
            logDebug("Failed to use InputSplitWithLocations.", e)
            None
        }
      case None => None
    }
    locs.getOrElse(hsplit.getLocations.filter(_ != "localhost"))
  }

??： 如果不写HadoopRDD.SPLIT... 则找不到SPLIT_INFO_REFLECTIONS

locs有可能是Some或者None, 则getOrElse，传进去一个函数，即去掉本地节点

private[spark] val SPLIT_INFO_REFLECTIONS: Option[SplitInfoReflections] = try {
    Some(new SplitInfoReflections)
  } catch {
    case e: Exception =>
      logDebug("SplitLocationInfo and other new Hadoop classes are " +
          "unavailable. Using the older Hadoop location info code.", e)
      None
  }

  private[spark] class SplitInfoReflections {
    val inputSplitWithLocationInfo =
      Class.forName("org.apache.hadoop.mapred.InputSplitWithLocationInfo")
    val getLocationInfo = inputSplitWithLocationInfo.getMethod("getLocationInfo")
    val newInputSplit = Class.forName("org.apache.hadoop.mapreduce.InputSplit")
    val newGetLocationInfo = newInputSplit.getMethod("getLocationInfo")
    val splitLocationInfo = Class.forName("org.apache.hadoop.mapred.SplitLocationInfo")
    val isInMemory = splitLocationInfo.getMethod("isInMemory")
    val getLocation = splitLocationInfo.getMethod("getLocation")
  }