a scala remote actor exception

Question

i with a scala code like this for echo service.

import scala.actors.Actor import scala.actors.Actor._ import scala.actors.remote.RemoteActor._

class Echo extends Actor {
   def act() {
        alive(9010)
        register('myName, self)

     loop {
       react {
            case msg  =>  println(msg)
       }
     }
   }
}
object EchoServer  {

   def main(args: Array[String]): unit = {
        val echo = new Echo
        echo.start
        println("Echo server started")
   }
} 
EchoServer.main(null)

but there has some exception.

java.lang.NoClassDefFoundError: Main$$anon$1$Echo$$anonfun$act$1
 at Main$$anon$1$Echo.act((virtual file):16)
 at scala.actors.Reaction.run(Reaction.scala:76)
 at scala.actors.Actor$$anonfun$start$1.apply(Actor.scala:785)
 at scala.actors.Actor$$anonfun$start$1.apply(Actor.scala:783)
 at scala.actors.FJTaskScheduler2$$anon$1.run(FJTaskScheduler2.scala:160)
 at scala.actors.FJTask$Wrap.run(Unknown Source)
 at scala.actors.FJTaskRunner.scanWhileIdling(Unknown Source)
 at scala.actors.FJTaskRunner.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: Main$$anon$1$Echo$$anonfun$act$1
 at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
 at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
 ... 8 more

i don't konw how can cause it. by the way .my scala version is 2.7.5

Answer 1

ClassNotFoundException indicates that something was probably not compiled, that should have been compiled. How did you compile it? Manually using scalac ?

Try the following rm *.class scalac *.scala scala EchoServer .

The following works:

---

EchoServer.scala

import scala.actors.Actor
import scala.actors.Actor._
import scala.actors.remote.RemoteActor._

class Echo extends Actor {
   def act() {
        alive(9010)
        register('myName, self)

     loop {
       react {
            case msg  =>  println(msg)
       }
     }
   }
}

object EchoServer  {

   def main(args: Array[String]): unit = {
        val echo = new Echo
        echo.start
        println("Echo server started")
   }
} 

---

Client.scala

import scala.actors.Actor._
import scala.actors.remote.Node
import scala.actors.remote.RemoteActor._

object Client extends Application {
    override def main(args: Array[String]) {
        if (args.length < 1) {
            println("Usage: scala Client [msg]")
            return
        }

        actor {
            val remoteActor = select(Node("localhost", 9010), 'myName)

            remoteActor !? args(0) match {
                case msg => println( "Server's response is [" + msg + "]" )
            }
        }
    }
}

---

Command line:

rm *.class && scalac *.scala  && scala EchoServer

And in other terminal:

scala Client hello

Answer 2

You need to set the classloader on the remote actors.

Before the act() method, add the line:

RemoteActor.classLoader = getClass.getClassLoader

Why is setting the classloader necessary with Scala RemoteActors?