scala - Play 2 Scala - 使用 Iteratee 上传大型 CSV 文件以便 react 性地处理每一行的最佳方式

Question

我想使用 Play2 在 elasticsearch 上上传一个非常大的 CSV 文件(数百万行)。我编写了以下代码，效果很好。

我对跳过第一个块中的 http 响应 header 的方式不满意。应该有一种方法可以将这个 iteratee 与跳过 http header 并直接切换到 Done 状态的第一个 Iteratee 链接起来，但我还没有找到方法。

如果有人可以帮忙

object ReactiveFileUpload extends Controller {
  def upload = Action(BodyParser(rh => new CsvIteratee(isFirst = true))) {
    request =>
      Ok("File Processed")
  }
}

case class CsvIteratee(state: Symbol = 'Cont, input: Input[Array[Byte]] = Empty, lastChunk: String = "", isFirst: Boolean = false) extends Iteratee[Array[Byte], Either[Result, String]] {
  def fold[B](
               done: (Either[Result, String], Input[Array[Byte]]) => Promise[B],
               cont: (Input[Array[Byte]] => Iteratee[Array[Byte], Either[Result, String]]) => Promise[B],
               error: (String, Input[Array[Byte]]) => Promise[B]
               ): Promise[B] = state match {
    case 'Done =>
      done(Right(lastChunk), Input.Empty)

    case 'Cont => cont(in => in match {
      case in: El[Array[Byte]] => {
        // Retrieve the part that has not been processed in the previous chunk and copy it in front of the current chunk
        val content = lastChunk + new String(in.e)
        val csvBody =
          if (isFirst)
            // Skip http header if it is the first chunk
            content.drop(content.indexOf("\r\n\r\n") + 4)
          else content
        val csv = new CSVReader(new StringReader(csvBody), ';')
        val lines = csv.readAll
        // Process all lines excepted the last one since it is cut by the chunk
        for (line <- lines.init)
          processLine(line)
        // Put forward the part that has not been processed
        val last = lines.last.toList.mkString(";")
        copy(input = in, lastChunk = last, isFirst = false)
      }
      case Empty => copy(input = in, isFirst = false)
      case EOF => copy(state = 'Done, input = in, isFirst = false)
      case _ => copy(state = 'Error, input = in, isFirst = false)
    })

    case _ =>
      error("Unexpected state", input)

  }

  def processLine(line: Array[String]) = WS.url("http://localhost:9200/affa/na/").post(
    toJson(
      Map(
        "date" -> toJson(line(0)),
        "trig" -> toJson(line(1)),
        "code" -> toJson(line(2)),
        "nbjours" -> toJson(line(3).toDouble)
      )
    )
  )
}

Answer 1

要将两个迭代器链接在一起，请使用 flatMap .

val combinedIteratee = firstIteratee.flatMap(firstResult => secondIteratee)

或者，使用 a 来理解:

val combinedIteratee = for {
  firstResult <- firstIteratee
  secondResult <- secondIteratee
} yield secondResult

您可以使用 flatMap 将任意数量的迭代器排列在一起。

您可能想要执行以下操作:

val headerAndCsvIteratee = for {
  headerResult <- headerIteratee
  csvResult <- csvIteratee
} yield csvResult