Over a million developers have joined DZone.

Akka Samples with Scala and Spring

· Java Zone

What every Java engineer should know about microservices: Reactive Microservices Architecture.  Brought to you in partnership with Lightbend.

I was looking around recently for Akka samples with Spring and found a starter project which appeared to fit the bill well. The project however utilizesSpring-Scala which is an excellent project, but is no longer maintained. So I wanted to update the sample to use core Spring java libraries instead. So here is an attempt on a fork of this starter project with core Spring instead of Spring-scala. The code is available here.

The project utilizes Akka extensions to hook in Spring based dependency injection into Akka. 

Here is what the extension looks like:

package sample

import akka.actor.{ActorSystem, Props, Extension}
import org.springframework.context.ApplicationContext
 * The Extension implementation.
class SpringExtension extends Extension {
  var applicationContext: ApplicationContext = _

   * Used to initialize the Spring application context for the extension.
   * @param applicationContext
  def initialize(applicationContext: ApplicationContext) = {
    this.applicationContext = applicationContext

   * Create a Props for the specified actorBeanName using the
   * SpringActorProducer class.
   * @param actorBeanName  The name of the actor bean to create Props for
   * @return a Props that will create the named actor bean using Spring
  def props(actorBeanName: String): Props =
    Props(classOf[SpringActorProducer], applicationContext, actorBeanName)


object SpringExtension {
  def apply(system : ActorSystem )(implicit ctx: ApplicationContext) :  SpringExtension =  SpringExt(system).initialize(ctx)

So the extension wraps around a Spring application context. The extensions provides a props method which returns an Akka Props configuration object which uses the application context and the name which the actor is registered with Spring to return an instance of the Actor. The following is the SpringActorProducer:

package sample

import akka.actor.{Actor, IndirectActorProducer}
import org.springframework.context.ApplicationContext

class SpringActorProducer(ctx: ApplicationContext, actorBeanName: String) extends IndirectActorProducer {

  override def produce: Actor = ctx.getBean(actorBeanName, classOf[Actor])

  override def actorClass: Class[_ <: Actor] =


Given this base code, how does Spring find the actors, I have used scanning annotations to annotate the actors this way:

package sample.actor

import akka.actor.Actor
import sample.service.CountingService
import sample.SpringExtension._
import org.springframework.stereotype.Component
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.context.annotation.Scope
import akka.actor.ActorRef
import sample.SpringExtension
import org.springframework.context.ApplicationContext

class CountingCoordinating @Autowired() (implicit ctx: ApplicationContext) extends Actor {

  import sample.messages._

  var counter: Option[ActorRef] = None

  def receive = {
    case COUNT => countingActor() ! COUNT
    case g:GET => countingActor() ! g
  private def countingActor(): ActorRef = {
     if (counter.isEmpty) {
        val countingActorProp = SpringExtension(context.system).props("countingActor")
        counter = Some(context.actorOf(countingActorProp, "counter"))

class CountingActor @Autowired()(countingService: CountingService) extends Actor {

  import sample.messages._

  private var count = 0

  def receive = {
    case COUNT => count = countingService.increment(count)
    case GET(requester: ActorRef) => requester ! RESULT(count)

The CountingService is a simple service that gets injected in by Spring. The following is the main Spring Application configuration where all the wiring takes place:

import akka.actor.ActorSystem
import org.springframework.context.ApplicationContext
import org.springframework.context.annotation.Configuration
import org.springframework.context.annotation.Bean
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.context.annotation.ComponentScan

@ComponentScan(Array("sample.service", "sample.actor"))
class AppConfiguration {

  implicit var ctx: ApplicationContext = _;
   * Actor system singleton for this application.
  def actorSystem() = {
    val system = ActorSystem("AkkaScalaSpring")
    // initialize the application context in the Akka Spring Extension

To make use of this entire set-up in a sample program:

import akka.actor.{ActorRef, ActorSystem}
import sample.SpringExtension._
import scala.concurrent.duration._
import scala.concurrent._
import scala.util._
import sample.messages._
import org.springframework.context.annotation.AnnotationConfigApplicationContext
import akka.actor.Inbox

object Main extends App {
  // create a spring context
  implicit val ctx = new AnnotationConfigApplicationContext(classOf[AppConfiguration])

  import Config._

  // get hold of the actor system
  val system = ctx.getBean(classOf[ActorSystem])

  val inbox = Inbox.create(system)
  val prop = SpringExtension(system).props("countingCoordinatingActor")

  // use the Spring Extension to create props for a named actor bean
  val countingCoordinator = system.actorOf(prop, "counter")

  // tell it to count three times
  inbox.send(countingCoordinator, COUNT)
  inbox.send(countingCoordinator, COUNT)
  inbox.send(countingCoordinator, COUNT)
  inbox.send(countingCoordinator, GET(inbox.getRef()))
  val RESULT(count) = inbox.receive(5.seconds)

  println(s"Got $count")


Microservices for Java, explained. Revitalize your legacy systems (and your career) with Reactive Microservices Architecture, a free O'Reilly book. Brought to you in partnership with Lightbend.


Published at DZone with permission of Biju Kunjummen, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}