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

This example Akka source code file (DynamicAccess.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, anyref, class, classcastexception, classloader, classtag, collection, dynamicaccess, invocationtargetexception, reflection, string, t, try, utilities

The DynamicAccess.scala Akka example source code

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

import scala.collection.immutable
import java.lang.reflect.InvocationTargetException
import scala.reflect.ClassTag
import scala.util.Try

/**
 * The DynamicAccess implementation is the class which is used for
 * loading all configurable parts of an actor system (the
 * [[akka.actor.ReflectiveDynamicAccess]] is the default implementation).
 *
 * This is an internal facility and users are not expected to encounter it
 * unless they are extending Akka in ways which go beyond simple Extensions.
 */
abstract class DynamicAccess {
  /**
   * Convenience method which given a `Class[_]` object and a constructor description
   * will create a new instance of that class.
   *
   * {{{
   * val obj = DynamicAccess.createInstanceFor(clazz, Seq(classOf[Config] -> config, classOf[String] -> name))
   * }}}
   */
  def createInstanceFor[T: ClassTag](clazz: Class[_], args: immutable.Seq[(Class[_], AnyRef)]): Try[T]

  /**
   * Obtain a `Class[_]` object loaded with the right class loader (i.e. the one
   * returned by `classLoader`).
   */
  def getClassFor[T: ClassTag](fqcn: String): Try[Class[_ <: T]]

  /**
   * Obtain an object conforming to the type T, which is expected to be
   * instantiated from a class designated by the fully-qualified class name
   * given, where the constructor is selected and invoked according to the
   * `args` argument. The exact usage of args depends on which type is requested,
   * see the relevant requesting code for details.
   */
  def createInstanceFor[T: ClassTag](fqcn: String, args: immutable.Seq[(Class[_], AnyRef)]): Try[T]

  /**
   * Obtain the Scala “object” instance for the given fully-qualified class name, if there is one.
   */
  def getObjectFor[T: ClassTag](fqcn: String): Try[T]

  /**
   * This is the class loader to be used in those special cases where the
   * other factory method are not applicable (e.g. when constructing a ClassLoaderBinaryInputStream).
   */
  def classLoader: ClassLoader
}

/**
 * This is the default [[akka.actor.DynamicAccess]] implementation used by [[akka.actor.ExtendedActorSystem]]
 * unless overridden. It uses reflection to turn fully-qualified class names into `Class[_]` objects
 * and creates instances from there using `getDeclaredConstructor()` and invoking that. The class loader
 * to be used for all this is determined by the actor system’s class loader by default.
 */
class ReflectiveDynamicAccess(val classLoader: ClassLoader) extends DynamicAccess {

  override def getClassFor[T: ClassTag](fqcn: String): Try[Class[_ <: T]] =
    Try[Class[_ <: T]]({
      val c = Class.forName(fqcn, false, classLoader).asInstanceOf[Class[_ <: T]]
      val t = implicitly[ClassTag[T]].runtimeClass
      if (t.isAssignableFrom(c)) c else throw new ClassCastException(t + " is not assignable from " + c)
    })

  override def createInstanceFor[T: ClassTag](clazz: Class[_], args: immutable.Seq[(Class[_], AnyRef)]): Try[T] =
    Try {
      val types = args.map(_._1).toArray
      val values = args.map(_._2).toArray
      val constructor = clazz.getDeclaredConstructor(types: _*)
      constructor.setAccessible(true)
      val obj = constructor.newInstance(values: _*)
      val t = implicitly[ClassTag[T]].runtimeClass
      if (t.isInstance(obj)) obj.asInstanceOf[T] else throw new ClassCastException(clazz.getName + " is not a subtype of " + t)
    } recover { case i: InvocationTargetException if i.getTargetException ne null ⇒ throw i.getTargetException }

  override def createInstanceFor[T: ClassTag](fqcn: String, args: immutable.Seq[(Class[_], AnyRef)]): Try[T] =
    getClassFor(fqcn) flatMap { c ⇒ createInstanceFor(c, args) }

  override def getObjectFor[T: ClassTag](fqcn: String): Try[T] = {
    val classTry =
      if (fqcn.endsWith("$")) getClassFor(fqcn)
      else getClassFor(fqcn + "$") recoverWith { case _ ⇒ getClassFor(fqcn) }
    classTry flatMap { c ⇒
      Try {
        val module = c.getDeclaredField("MODULE$")
        module.setAccessible(true)
        val t = implicitly[ClassTag[T]].runtimeClass
        module.get(null) match {
          case null                  ⇒ throw new NullPointerException
          case x if !t.isInstance(x) ⇒ throw new ClassCastException(fqcn + " is not a subtype of " + t)
          case x: T                  ⇒ x
        }
      } recover { case i: InvocationTargetException if i.getTargetException ne null ⇒ throw i.getTargetException }
    }
  }
}