Scala：将文件读取为无限/异步行流

Question

I have a file /files/somelog.log that is continuously written to by some other process. What I want to do is to read that file as a (never-ending) stream and respond to it whenever there is a new log line available.

val logStream: Stream[String] = readAsStream("/files/somelog.log")
logStream.foreach { line: String => println(line) }

So, immediately when the other process writes anther line to the logfile, I expect the println above to go off (and keep going off).

However, that doesn't seem to be how the default Stream-type works. Scala's Stream isn't async, it's just lazy. What I'm probably looking for is something similar to what akka streams offers (I think). But Akka is so huge (150MB!) - I don't want to pull in so many new things that I don't need just to do something this simple/basic. Is there really no other (tiny!) library or technique I can use?

Answer 1

If you simply want to tail the file you could use Tailer from Apache Commons IO:

val l = new TailerListenerAdapter() {
    override def handle(line: String): Unit = println(line)
}

val tail = Tailer.create(new File("file.txt"), l)

Answer 2

I'm not actually recommending this, but you could roll your own.

def nextLine( itr: Iterator[String] ): String = {
  while (!itr.hasNext) Thread.sleep(2000)
  itr.next
}
. . .
val log = io.Source.fromFile("/files/somelog.log").getLines
val logTxt = nextLine( log )  // will block until next line is available
. . .