Scala example source code file (ProcessLogger.scala)

This example Scala source code file (ProcessLogger.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

file, fileoutputstream, fileprocesslogger, flushable, outputstreamwriter, printwriter, processlogger, string, t, unit

The ProcessLogger.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package sys
package process

import java.io._

/** Encapsulates the output and error streams of a running process. This is used
  * by [[scala.sys.process.ProcessBuilder]] when starting a process, as an
  * alternative to [[scala.sys.process.ProcessIO]], which can be more difficult
  * to use. Note that a `ProcessLogger` will be used to create a `ProcessIO`
  * anyway. The object `BasicIO` has some functions to do that.
  *
  * Here is an example that counts the number of lines in the normal and error
  * output of a process:
  * {{{
  * import scala.sys.process._
  *
  * var normalLines = 0
  * var errorLines = 0
  * val countLogger = ProcessLogger(line => normalLines += 1,
  *                                 line => errorLines += 1)
  * "find /etc" ! countLogger
  * }}}
  *
  *  @see [[scala.sys.process.ProcessBuilder]]
  */
trait ProcessLogger {
  /** Will be called with each line read from the process output stream.
   */
  def out(s: => String): Unit

  /** Will be called with each line read from the process error stream.
   */
  def err(s: => String): Unit

  /** If a process is begun with one of these `ProcessBuilder` methods:
   *  {{{
   *    def !(log: ProcessLogger): Int
   *    def !<(log: ProcessLogger): Int
   *  }}}
   *  The run will be wrapped in a call to buffer.  This gives the logger
   *  an opportunity to set up and tear down buffering.  At present the
   *  library implementations of `ProcessLogger` simply execute the body
   *  unbuffered.
   */
  def buffer[T](f: => T): T
}

/** A [[scala.sys.process.ProcessLogger]] that writes output to a file. */
class FileProcessLogger(file: File) extends ProcessLogger with Closeable with Flushable {
  private val writer = (
    new PrintWriter(
      new BufferedWriter(
        new OutputStreamWriter(
          new FileOutputStream(file, true)
        )
      )
    )
  )
  def out(s: => String): Unit = writer println s
  def err(s: => String): Unit = writer println s
  def buffer[T](f: => T): T = f
  def close(): Unit = writer.close()
  def flush(): Unit = writer.flush()
}

/** Provides factories to create [[scala.sys.process.ProcessLogger]], which
 *  are used to capture output of [[scala.sys.process.ProcessBuilder]] commands
 *  when run.
 */
object ProcessLogger {
  /** Creates a [[scala.sys.process.ProcessLogger]] that redirects output to a `java.io.File`. */
  def apply(file: File): FileProcessLogger = new FileProcessLogger(file)

  /** Creates a [[scala.sys.process.ProcessLogger]] that sends all output, standard and error,
   *  to the passed function.
   */
  def apply(fn: String => Unit): ProcessLogger = apply(fn, fn)

  /** Creates a [[scala.sys.process.ProcessLogger]] that sends all output to the corresponding
   *  function.
   *
   *  @param fout  This function will receive standard outpout.
   *
   *  @param ferr  This function will receive standard error.
   */
  def apply(fout: String => Unit, ferr: String => Unit): ProcessLogger =
    new ProcessLogger {
      def out(s: => String): Unit = fout(s)
      def err(s: => String): Unit = ferr(s)
      def buffer[T](f: => T): T = f
    }
}