Akka, Concurrency, etc.

Serializer minimal example

Overview

You can find the code and instruction to run the example at GitHub.

Akka Serialization

Akka doc's serialization section says:

However, messages that have to escape the JVM to reach an actor running on a different host have to undergo some form of serialization (i.e. the objects have to be converted to and from byte arrays).

This example shows a simplified version, but still the core of what Akka serialization does - (i.e.) how Serialization Akka extention class, Serializer, and the message you want to serialize/deserialize work together.

Serializer configuration

First, you need to define your serializer class, extending Serializer.

import akka.serialization.Serializer

case class MyMessage(str1: String, str2: String)


class MySerializer extends Serializer {
  ...
}

Then you need configuration which binds your MySerializer to the MyMessage type. Note the common mymessage key which defines the binding.

//application.conf
akka {
  actor {
    serializers {
      mymessage = "example.MySerializer"
    }                                     
    serialization-bindings {              
      "example.MyMessage" = mymessage     
    }
  }
}

Next, you should define toBinary and fromBinary inside MySerializer to handle serialization and deserialization of MyMessage instances.

  def toBinary(obj: AnyRef): Array[Byte] = {
    obj match {
      case msg: MyMessage => 
        (msg.str1 + "|" + msg.str2).getBytes(StandardCharsets.UTF_8)
    }
  }
  def fromBinary(bytes: Array[Byte], clazz: Option[Class[_]]): AnyRef = {
    val repString = new String(bytes, StandardCharsets.UTF_8)
    // '|' is enclosed in single quotes = Char, not 
    val arr: Array[String] = repString.split('|') String
    new MyMessage(arr(0), arr(1))
  }

The below piece of code is the simplied version of what Akka does, when serializing a message.

val system = akka.actor.ActorSystem("example", ConfigFactory.load())
val original = MyMessage("aaa", "bbb")
val serialization = SerializationExtension(system)

//serialization by toBinary
val bytes = serializer.toBinary(original)

//de-serialization by fromBinary
val restored = serializer.fromBinary(bytes, manifest = None)

When you are (e.g.) sending a message to a remote JVM, this is done under the ground and you don't explicitly call SerializationExtension(system), toBinary and fromBinary yourself, but this example is to show what's done by Akka in the simple form.

Instruction to run the example

> git clone https://github.com/richardimaoka/resources.git
> cd resources
> cd serialize-minimal
> sbt
> runMain example.Main

Output

Some println calls are inserted in the complete example at GitHub to illustrate the behavior

[info] Running example.Main
Serializer for class example.MyMessage = example.MySerializer@254b2a65
MySerializer: toBinary(MyMessage(aaa,bbb)) is called
MySerializer: fromBinary(979797124989898) is called
original = MyMessage(aaa,bbb), class = class example.MyMessage
restored = MyMessage(aaa,bbb), class = class example.MyMessage
[success] Total time: 1 s, completed Jan 23, 2018 9:48:55 PM

References

  • Official documentation of Akka serialization at https://doc.akka.io/docs/akka/2.5/serialization.html
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