Akka/Scala example source code file (Main.scala)

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

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

Akka tags/keywords

actor, akka, collection, dnnnn, dnnnnn, file, kernel, nnnn, nnnnn, zz, zzz, zzzz, zzzzzz

The Main.scala Akka example source code

/**
 * Copyright (C) 2009-2014 Typesafe Inc. <http://www.typesafe.com>
 */

package akka.kernel

import akka.actor.ActorSystem
import java.io.File
import java.lang.Boolean.getBoolean
import java.net.URLClassLoader
import java.util.jar.JarFile
import scala.collection.immutable
import scala.collection.JavaConverters._

/**
 * To use the microkernel at least one 'boot class' needs to be specified.
 * A boot class implements this interface ([[akka.kernel.Bootable]]) and
 * must have an empty default constructor.
 *
 * ActorSystems can be created within the boot class.
 *
 * An example of a simple boot class:
 * {{{
 * class BootApp extends Bootable {
 *   val system = ActorSystem("app")
 *
 *   def startup = {
 *     system.actorOf(Props[FirstActor]) ! FirstMessage
 *   }
 *
 *   def shutdown = {
 *     system.shutdown()
 *   }
 * }
 * }}}
 *
 * Boot classes are specified as main arguments to the microkernel.
 *
 * For example, using the akka script an application can be started with
 * the following at the command line:
 * {{{
 * bin/akka org.app.BootApp
 * }}}
 */
trait Bootable {
  /**
   * Callback run on microkernel startup.
   * Create initial actors and messages here.
   */
  def startup(): Unit

  /**
   * Callback run on microkernel shutdown.
   * Shutdown actor systems here.
   */
  def shutdown(): Unit
}

/**
 * Main class for running the microkernel.
 */
object Main {
  private val quiet = getBoolean("akka.kernel.quiet")

  private def log(s: String) = if (!quiet) println(s)

  def main(args: Array[String]) = {
    if (args.isEmpty) {
      log("[error] No boot classes specified")
      System.exit(1)
    }

    log(banner)
    log("Starting Akka...")
    log("Running Akka " + ActorSystem.Version)

    val classLoader = createClassLoader()

    Thread.currentThread.setContextClassLoader(classLoader)

    val bootClasses: immutable.Seq[String] = args.to[immutable.Seq]
    val bootables: immutable.Seq[Bootable] = bootClasses map { c ⇒ classLoader.loadClass(c).newInstance.asInstanceOf[Bootable] }

    for (bootable ← bootables) {
      log("Starting up " + bootable.getClass.getName)
      bootable.startup()
    }

    addShutdownHook(bootables)

    log("Successfully started Akka")
  }

  private def createClassLoader(): ClassLoader = {
    if (ActorSystem.GlobalHome.isDefined) {
      val home = ActorSystem.GlobalHome.get
      val deploy = new File(home, "deploy")
      if (deploy.exists) {
        loadDeployJars(deploy)
      } else {
        log("[warning] No deploy dir found at " + deploy)
        Thread.currentThread.getContextClassLoader
      }
    } else {
      log("[warning] Akka home is not defined")
      Thread.currentThread.getContextClassLoader
    }
  }

  private def loadDeployJars(deploy: File): ClassLoader = {
    val jars = deploy.listFiles.filter(_.getName.endsWith(".jar"))

    val nestedJars = jars flatMap { jar ⇒
      val jarFile = new JarFile(jar)
      val jarEntries = jarFile.entries.asScala.toArray.filter(_.getName.endsWith(".jar"))
      jarEntries map { entry ⇒ new File("jar:file:%s!/%s" format (jarFile.getName, entry.getName)) }
    }

    val urls = (jars ++ nestedJars) map { _.toURI.toURL }

    urls foreach { url ⇒ log("Deploying " + url) }

    new URLClassLoader(urls, Thread.currentThread.getContextClassLoader)
  }

  private def addShutdownHook(bootables: immutable.Seq[Bootable]): Unit = {
    Runtime.getRuntime.addShutdownHook(new Thread(new Runnable {
      def run = {
        log("")
        log("Shutting down Akka...")

        for (bootable ← bootables) {
          log("Shutting down " + bootable.getClass.getName)
          bootable.shutdown()
        }

        log("Successfully shut down Akka")
      }
    }))
  }

  private def banner = """
==============================================================================

                                                   ZZ:
                                                  ZZZZ
                                                 ZZZZZZ
                                                ZZZ' ZZZ
                                       ~7      7ZZ'   ZZZ
                                      :ZZZ:   IZZ'     ZZZ
                                     ,OZZZZ.~ZZ?        ZZZ
                                    ZZZZ' 'ZZZ$          ZZZ
                           .       $ZZZ   ~ZZ$            ZZZ
                         .=Z?.   .ZZZO   ~ZZ7              OZZ
                        .ZZZZ7..:ZZZ~   7ZZZ                ZZZ~
                      .$ZZZ$Z+.ZZZZ    ZZZ:                  ZZZ$
                   .,ZZZZ?'  =ZZO=   .OZZ                     'ZZZ
                 .$ZZZZ+   .ZZZZ    IZZZ                        ZZZ$
               .ZZZZZ'   .ZZZZ'   .ZZZ$                          ?ZZZ
            .ZZZZZZ'   .OZZZ?    ?ZZZ                             'ZZZ$
        .?ZZZZZZ'    .ZZZZ?    .ZZZ?                                'ZZZO
    .+ZZZZZZ?'    .7ZZZZ'    .ZZZZ                                    :ZZZZ
 .ZZZZZZ$'     .?ZZZZZ'   .~ZZZZ                                        'ZZZZ.


                      NNNNN              $NNNN+
                      NNNNN              $NNNN+
                      NNNNN              $NNNN+
                      NNNNN              $NNNN+
                      NNNNN              $NNNN+
    =NNNNNNNNND$      NNNNN     DDDDDD:  $NNNN+     DDDDDN     NDDNNNNNNNN,
   NNNNNNNNNNNNND     NNNNN    DNNNNN    $NNNN+   8NNNNN=    :NNNNNNNNNNNNNN
  NNNNN$    DNNNNN    NNNNN  $NNNNN~     $NNNN+  NNNNNN      NNNNN,   :NNNNN+
   ?DN~      NNNNN    NNNNN MNNNNN       $NNNN+:NNNNN7        $ND      =NNNNN
            DNNNNN    NNNNNDNNNN$        $NNNNDNNNNN                  :DNNNNN
     ZNDNNNNNNNNND    NNNNNNNNNND,       $NNNNNNNNNNN           DNDNNNNNNNNNN
   NNNNNNNDDINNNNN    NNNNNNNNNNND       $NNNNNNNNNNND       ONNNNNNND8+NNNNN
 :NNNND      NNNNN    NNNNNN  DNNNN,     $NNNNNO 7NNNND     NNNNNO     :NNNNN
 DNNNN       NNNNN    NNNNN    DNNNN     $NNNN+   8NNNNN    NNNNN      $NNNNN
 DNNNNO     NNNNNN    NNNNN     NNNNN    $NNNN+    NNNNN$   NNNND,    ,NNNNND
  NNNNNNDDNNNNNNNN    NNNNN     =NNNNN   $NNNN+     DNNNN?  DNNNNNNDNNNNNNNND
   NNNNNNNNN  NNNN$   NNNNN      8NNNND  $NNNN+      NNNNN=  ,DNNNNNNND NNNNN$

==============================================================================
"""
}