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

This example Akka source code file (Serializer.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, array, boolean, bytearrayserializer, currentsystem, extendedactorsystem, javaserializer, nullserializer, option, serialization, serialize, serializer, util, utilities

The Serializer.scala Akka example source code

package akka.serialization

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

import java.io.{ ObjectOutputStream, ByteArrayOutputStream, ObjectInputStream, ByteArrayInputStream }
import java.util.concurrent.Callable
import akka.util.ClassLoaderObjectInputStream
import akka.actor.ExtendedActorSystem
import scala.util.DynamicVariable
import akka.serialization.JavaSerializer.CurrentSystem

/**
 * A Serializer represents a bimap between an object and an array of bytes representing that object.
 *
 * Serializers are loaded using reflection during [[akka.actor.ActorSystem]]
 * start-up, where two constructors are tried in order:
 *
 * <ul>
 * <li>taking exactly one argument of type [[akka.actor.ExtendedActorSystem]];
 * this should be the preferred one because all reflective loading of classes
 * during deserialization should use ExtendedActorSystem.dynamicAccess (see
 * [[akka.actor.DynamicAccess]]), and</li>
 * <li>without arguments, which is only an option if the serializer does not
 * load classes using reflection.</li>
 * </ul>
 *
 * <b>Be sure to always use the PropertyManager for loading classes!</b> This is necessary to
 * avoid strange match errors and inequalities which arise from different class loaders loading
 * the same class.
 */
trait Serializer {

  /**
   * Completely unique value to identify this implementation of Serializer, used to optimize network traffic
   * Values from 0 to 16 is reserved for Akka internal usage
   */
  def identifier: Int

  /**
   * Serializes the given object into an Array of Byte
   */
  def toBinary(o: AnyRef): Array[Byte]

  /**
   * Returns whether this serializer needs a manifest in the fromBinary method
   */
  def includeManifest: Boolean

  /**
   * Produces an object from an array of bytes, with an optional type-hint;
   * the class should be loaded using ActorSystem.dynamicAccess.
   */
  def fromBinary(bytes: Array[Byte], manifest: Option[Class[_]]): AnyRef

  /**
   * Java API: deserialize without type hint
   */
  final def fromBinary(bytes: Array[Byte]): AnyRef = fromBinary(bytes, None)

  /**
   * Java API: deserialize with type hint
   */
  final def fromBinary(bytes: Array[Byte], clazz: Class[_]): AnyRef = fromBinary(bytes, Option(clazz))
}

/**
 * Java API for creating a Serializer: make sure to include a constructor which
 * takes exactly one argument of type [[akka.actor.ExtendedActorSystem]], because
 * that is the preferred constructor which will be invoked when reflectively instantiating
 * the JSerializer (also possible with empty constructor).
 */
abstract class JSerializer extends Serializer {
  final def fromBinary(bytes: Array[Byte], manifest: Option[Class[_]]): AnyRef =
    fromBinaryJava(bytes, manifest.orNull)

  /**
   * This method must be implemented, manifest may be null.
   */
  protected def fromBinaryJava(bytes: Array[Byte], manifest: Class[_]): AnyRef
}

object NullSerializer extends NullSerializer

object JavaSerializer {

  /**
   * This holds a reference to the current ActorSystem (the surrounding context)
   * during serialization and deserialization.
   *
   * If you are using Serializers yourself, outside of SerializationExtension,
   * you'll need to surround the serialization/deserialization with:
   *
   * currentSystem.withValue(system) {
   *   ...code...
   * }
   *
   * or
   *
   * currentSystem.withValue(system, callable)
   */
  val currentSystem = new CurrentSystem
  final class CurrentSystem extends DynamicVariable[ExtendedActorSystem](null) {
    /**
     * Java API: invoke the callable with the current system being set to the given value for this thread.
     *
     * @param value - the current value under the call to callable.call()
     * @param callable - the operation to be performed
     * @tparam S - the return type
     * @return the result of callable.call()
     */
    def withValue[S](value: ExtendedActorSystem, callable: Callable[S]): S = super.withValue[S](value)(callable.call)
  }
}

/**
 * This Serializer uses standard Java Serialization
 */
class JavaSerializer(val system: ExtendedActorSystem) extends Serializer {

  def includeManifest: Boolean = false

  def identifier = 1

  def toBinary(o: AnyRef): Array[Byte] = {
    val bos = new ByteArrayOutputStream
    val out = new ObjectOutputStream(bos)
    JavaSerializer.currentSystem.withValue(system) { out.writeObject(o) }
    out.close()
    bos.toByteArray
  }

  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]]): AnyRef = {
    val in = new ClassLoaderObjectInputStream(system.dynamicAccess.classLoader, new ByteArrayInputStream(bytes))
    val obj = JavaSerializer.currentSystem.withValue(system) { in.readObject }
    in.close()
    obj
  }
}

/**
 * This is a special Serializer that Serializes and deserializes nulls only
 */
class NullSerializer extends Serializer {
  val nullAsBytes = Array[Byte]()
  def includeManifest: Boolean = false
  def identifier = 0
  def toBinary(o: AnyRef) = nullAsBytes
  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]]): AnyRef = null
}

/**
 * This is a special Serializer that Serializes and deserializes byte arrays only,
 * (just returns the byte array unchanged/uncopied)
 */
class ByteArraySerializer extends Serializer {
  def includeManifest: Boolean = false
  def identifier = 4
  def toBinary(o: AnyRef) = o match {
    case null           ⇒ null
    case o: Array[Byte] ⇒ o
    case other          ⇒ throw new IllegalArgumentException("ByteArraySerializer only serializes byte arrays, not [" + other + "]")
  }
  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]]): AnyRef = bytes
}