Turn on or off the standard out & error streams of a JVM program, written in Scala.

OnOffStdOutErrG.scala

object OnOffStdOutErrG {

  import java.io.{OutputStream, PrintStream}

  private[this] val (originalStdOut, originalStdErr) = (System.out, System.err)
  
  /** A PrintStream for "/dev/null": all write() invocations are no-ops. */
  val devnull = new PrintStream(
      new OutputStream() {
        override def write(ignore: Int): Unit = { /* nothing !! */ }
      }
    )

  /** Sets std{out,err} to "/dev/null", returns the original std{out,err} streams. */
  @synchronized def off(): Unit = {
    System.setOut(devnull)
    System.setErr(devnull)
  }

  /** Sets std{out,err} to the original streams. */
  @synchronized def on(): Unit = {
    System.setOut(originalStdOut)
    System.setErr(originalStdErr)
  }
}