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 The project however utilizes Spring-Scala which is an excellent project, but is no longer maintained.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
 this
 }

 /**
 * 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] =
 ctx.getType(actorBeanName).asInstanceOf[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

@Component("countingCoordinatingActor")
@Scope("prototype")
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"))
 } 
 
 counter.get
 }
 
}


@Component("countingActor")
@Scope("prototype")
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

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

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

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")
 system.shutdown
 system.awaitTermination
}

References:

• Most of the code is thanks to the akka-java-spring project available here.
• The project is originally forked from here