Could not execute this Akka actor based test code - scala

Question

I am new to Scala Akka actor. Based on the akka tutorial example on their website,i coded a similar example with just printing messages with the time they started. But the code does not get executed in my eclipse IDE.
import akka.actor.Actor
import akka.actor.ActorRef
import scala.collection.mutable.ListBuffer
import akka.actor.Props
import akka.routing.RoundRobinRouter
import akka.actor.ActorSystem
object AkaObj extends App{
process()
sealed trait PiMessage
case class Work(value:String) extends PiMessage
case class printComp(valu:String)extends PiMessage
case object Start extends PiMessage
case class ListObj(cont:Seq[String]) extends PiMessage
class Worker extends Actor{
def receive()={
case Work(value:String)=>
println(value)
sender ! printComp(value)
}
}
class Master(listener: ActorRef) extends Actor{
val nrOfWorkers = 10
var counter = 0
var lis = ListBuffer[String]()
val workerRouter = context.actorOf(
Props[Worker].withRouter(RoundRobinRouter(nrOfWorkers)), name = "workerRouter")
def receive()={
//handle message
case Start=>workerRouter ! Work("Start now " + System.currentTimeMillis())
case printComp(value:String)=> {
counter+=1
lis.append(counter+"-"+value)
if(counter >=10)
listener ! ListObj(lis.toSeq)
// Stops this actor and all its supervised children
context.stop(self)
}
}
}
class Listener extends Actor{
def receive()={
case ListObj(cont:Seq[String])=>
println("Completed " +cont)
context.system.shutdown()
}
}
def process(){
// Create an Akka system
val system = ActorSystem("PiSystem")
// create the result listener, which will print the result and shutdown the system
val listener = system.actorOf(Props[Listener], name = "listener")
// create the master
val master = system.actorOf(Props(new Master(listener)),
name = "master")
// start the calculation
master ! Start
}
}
Issue: The error message i get is: "Error: Could not find or load main class AkaObj"
It does not even compiling i think. When i run the project,that's the message i get.

Answer 1

Actually, I managed to run your code just after dependencies were resolved. So the problem is in your environment configuration. I use Intellij Idea IDE.
Try this Eclipse Error: Could not find or load main class

Answer 2

The actual problem is the use of object AkaObj extends App. When programming scala I have noticed that using scala.App is restricted to simple programs (at least in IDEs). As soon as you start defining objects and classes inside scala.App Eclipse starts complaining about not finding the entry point of the program.
Try to fix this as follows:
import akka.actor.Actor
import akka.actor.ActorRef
import scala.collection.mutable.ListBuffer
import akka.actor.Props
import akka.routing.RoundRobinRouter
import akka.actor.ActorSystem
object AkaObj {
def main(args:Array[String]) {
process()
}
def process() {
// Create an Akka system
val system = ActorSystem("PiSystem")
// create the result listener, which will print the result and shutdown the system
val listener = system.actorOf(Props[Listener], name = "listener")
// create the master
val master = system.actorOf(Props(new Master(listener)),
name = "master")
// start the calculation
master ! Start
}
sealed trait PiMessage
case class Work(value:String) extends PiMessage
case class printComp(valu:String)extends PiMessage
case object Start extends PiMessage
case class ListObj(cont:Seq[String]) extends PiMessage
class Worker extends Actor{
def receive()={
case Work(value:String)=>
println(value)
sender ! printComp(value)
}
}
class Master(listener: ActorRef) extends Actor{
val nrOfWorkers = 10
var counter = 0
var lis = ListBuffer[String]()
val workerRouter = context.actorOf(
Props[Worker].withRouter(RoundRobinRouter(nrOfWorkers)), name = "workerRouter")
def receive()={
//handle message
case Start=>workerRouter ! Work("Start now " + System.currentTimeMillis())
case printComp(value:String)=> {
counter+=1
lis.append(counter+"-"+value)
if(counter >=10)
listener ! ListObj(lis.toSeq)
// Stops this actor and all its supervised children
context.stop(self)
}
}
}
class Listener extends Actor{
def receive()={
case ListObj(cont:Seq[String])=>
println("Completed " +cont)
context.system.shutdown()
}
}
}
Using def main(args:Array[String]) fixes the problem in most cases.