FileWatch.scala

val fs = java.nio.file.FileSystems.getDefault
val w = fs.newWatchService()
val dir = userHome/"Documents"/"jack"
val name = "fifo.log"
val p = dir.toPath
val wk = p.register(w, java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY)

new Thread {
  override def run(): Unit = {
    val f = dir / name
    var lastLen = f.length()
    while (true) {
      val wk2 = w.take()
      import scala.collection.JavaConversions._
      val changed = wk2.pollEvents.exists { evt =>
        // we only registered "ENTRY_MODIFY" so the context is always a Path.
        val p = evt.context.asInstanceOf[java.nio.file.Path]
        p.endsWith(name)
      }
      val valid = wk2.reset()
      if (!valid) {
        println("Key has been unregistered.")
        return
      }
      if (changed) {
        val newLen = f.length()
        val raf = new java.io.RandomAccessFile(f, "r")
        try {
          raf.seek(lastLen)
          val len = (newLen - lastLen).toInt
          val arr = new Array[Byte](len)
          raf.readFully(arr)
          val s = new String(arr, "UTF-8")
          println(":::: GOT ::::")
          println(s)
        } finally {
          raf.close()          
        }
        lastLen = newLen
      }
    }
  }
      
  start()
}