Scala example source code file (SystemProperties.scala)

This example Scala source code file (SystemProperties.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

accesscontrolexception, booleanprop, collection, iterator, none, p, prop, some, string, systemproperties, t

The SystemProperties.scala Scala example source code

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

package scala
package sys

import scala.collection.{ mutable, Iterator }
import scala.collection.JavaConverters._
import java.security.AccessControlException
import scala.language.implicitConversions


/** A bidirectional map wrapping the java System properties.
 *  Changes to System properties will be immediately visible in the map,
 *  and modifications made to the map will be immediately applied to the
 *  System properties.  If a security manager is in place which prevents
 *  the properties from being read or written, the AccessControlException
 *  will be caught and discarded.
 *
 *  @author Paul Phillips
 *  @version 2.9
 *  @since   2.9
 */
class SystemProperties
extends mutable.AbstractMap[String, String]
   with mutable.Map[String, String] {

  override def empty = new SystemProperties
  override def default(key: String): String = null

  def iterator: Iterator[(String, String)] =
    wrapAccess(System.getProperties().asScala.iterator) getOrElse Iterator.empty
  def get(key: String) =
    wrapAccess(Option(System.getProperty(key))) flatMap (x => x)
  override def contains(key: String) =
    wrapAccess(super.contains(key)) exists (x => x)

  def -= (key: String): this.type = { wrapAccess(System.clearProperty(key)) ; this }
  def += (kv: (String, String)): this.type = { wrapAccess(System.setProperty(kv._1, kv._2)) ; this }

  def wrapAccess[T](body: => T): Option[T] =
    try Some(body) catch { case _: AccessControlException => None }
}

/** The values in SystemProperties can be used to access and manipulate
 *  designated system properties.  See `scala.sys.Prop` for particulars.
 *  @example {{{
 *    if (!headless.isSet) headless.enable()
 *  }}}
 */
object SystemProperties {
  /** An unenforceable, advisory only place to do some synchronization when
   *  mutating system properties.
   */
  def exclusively[T](body: => T) = this synchronized body

  implicit def systemPropertiesToCompanion(p: SystemProperties): SystemProperties.type = this
  private lazy val propertyHelp = mutable.Map[String, String]()
  private def addHelp[P <: Prop[_]](p: P, helpText: String): P = {
    propertyHelp(p.key) = helpText
    p
  }
  private def bool(key: String, helpText: String): BooleanProp = addHelp[BooleanProp](
    if (key startsWith "java.") BooleanProp.valueIsTrue(key) else BooleanProp.keyExists(key),
    helpText
  )
  def help(key: String) = propertyHelp.getOrElse(key, "")

  // Todo: bring some sanity to the intersection of system properties aka "mutable
  // state shared by everyone and everything" and the reality that there is no other
  // mechanism for accomplishing some things on the jvm.
  lazy val headless            = bool("java.awt.headless", "system should not utilize a display device")
  lazy val preferIPv4Stack     = bool("java.net.preferIPv4Stack", "system should prefer IPv4 sockets")
  lazy val preferIPv6Addresses = bool("java.net.preferIPv6Addresses", "system should prefer IPv6 addresses")
  lazy val noTraceSupression   = bool("scala.control.noTraceSuppression", "scala should not suppress any stack trace creation")
}