Read a file while it's being written (good for analysis of streaming data)

LiveReader.scala

import java.io.BufferedInputStream
import java.io.BufferedReader
import java.io.FileInputStream
import java.io.IOException
import java.io.InputStreamReader

import java.lang.Thread
import java.nio.charset.StandardCharsets

import scala.io.StdIn
import scala.Console

object LiveReader {

  var userInput    = ""
  var killedByUser = false
  var running      = true

  val filepath = "path/to/fileToBeRead.txt"
  val file     = new FileInputStream(filepath)
  val buffer   = new BufferedInputStream(file, 4096)
  val lines    = new BufferedReader(new InputStreamReader(buffer, StandardCharsets.UTF_8))
  var lastLine = ""

  def main(args: Array[String]) = {

    val countThread = new Thread {
      override def run {

        while (!killedByUser && running) {
          try {
//        to read char-by-char, use the BufferedInputStream by itself:
//          if (buffer.available() > 0) {
//            print(buffer.read().toChar)
            if(lines.ready()) {
              lastLine = lines.readLine()
              println(lastLine)
            } else {
              try {
                Thread.sleep(500) // check file every 500 ms
              } catch {
                case ex: InterruptedException => {
                  println("RealTime: file read interrupted!")
                  running = false
            } } }
          } catch {
            case ex: IOException => {
              println("RealTime: file read interrupted!")
              ex.printStackTrace()
    } } } } }

    countThread.start()
    println("Reading file...")

    /// run until the user hits the kill switch
    while(!killedByUser) {

      // listen for user input here [ http://bit.ly/2yd5Dl8 ]
      while (!Console.in.ready) {
        Thread.sleep(500) // check user input every 500 ms
      }

      // process user input here
      if(!killedByUser) {
        val userInput = StdIn.readLine()

        // echo user input
        print(f"  You entered: '$userInput': ")

        /// define user commands here

        if (List("q","Q","quit","Quit","QUIT","exit","EXIT","Exit","x","X") contains userInput) {
          print(f"  program terminated.\n\n")
          killedByUser = true

        } else if (List("l","L","line","Line","LINE") contains userInput) {
          print(f"  last line read was:\n    ${lastLine}\n\n")

        } else { // reset the Console if user enters nonsense
          print(f"  undefined command\n\n")
          Console.in.mark(0)
          Console.in.reset()
        }

        // do other stuff
      }
    }
  }
}