Serveur de travaux Spark avec Java

J'utilise spark avec java, et je veux utiliser spark Job-Server. Pour cela j'ai suivi tout dans ce lien : https://github.com/spark-jobserver/spark-jobserver

C'est la classe scala dans mon projet:

import _root_.spark.jobserver.SparkJob
import _root_.spark.jobserver.SparkJobValid
import _root_.spark.jobserver.SparkJobValidation
import com.typesafe.config._

import org.apache.spark._
import org.apache.spark.api.java.JavaSparkContext
import spark.jobserver.{SparkJob, SparkJobValid, SparkJobValidation}

object JavaWord extends SparkJob {
   def main(args: Array[String]) {
   val ctx = new SparkContext("local[4]", "JavaWordCount")
   val config = ConfigFactory.parseString("")

   val results = runJob(ctx, config)
   }

   override def validate(sc: SparkContext, config: Config): SparkJobValidation = {
      SparkJobValid;
   }

   override def runJob(sc: SparkContext, config: Config): Any = {
      val jsc = new JavaSparkContext(sc)
      val j = new JavaCount()
      return j.Mafonction(jsc: JavaSparkContext)
   }
  }

Et la classe Java "word wount"

import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaSparkContext;
import org.apache.spark.api.java.function.Function2;
import org.apache.spark.api.java.function.PairFunction;
import scala.Tuple2;
import java.io.Serializable;
import java.util.Arrays;  
import java.util.regex.Pattern;



public final class JavaCount implements Serializable {
public static Object main(String[] args) throws Exception {

    return null;
}

public Object Mafonction(JavaSparkContext sc){
    String s= "a a a a b b c a";
    JavaPairRDD<String, Integer>  lines = sc.parallelize(Arrays.asList(s.split(" "))).mapToPair(new PairFunction<String, String, Integer>() {
        @Override
        public Tuple2<String, Integer> call(String s) {
            return new Tuple2<String, Integer>(s, 1);
        }
    }).reduceByKey(new Function2<Integer, Integer, Integer>() {
        @Override
        public Integer call(Integer i1, Integer i2) {
            return i1 + i2;
        }
    });
    return lines.collect();
}
}

Mais quand je l'exécute, j'ai obtenu {[3] } avec cette erreur dans spark job-server:

> job-server[ERROR] Uncaught error from thread [JobServer-akka.actor.default-dispatcher-13]       shutting down JVM since 'akka.jvm-exit-on-fatal-error' is enabled for ActorSystem[JobServer]
job-server[ERROR] java.lang.IncompatibleClassChangeError: Implementing class
job-server[ERROR]   at java.lang.ClassLoader.defineClass1(Native Method)
job-server[ERROR]   at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
job-server[ERROR]   at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
job-server[ERROR]   at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
job-server[ERROR]   at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
job-server[ERROR]   at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
job-server[ERROR]   at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
job-server[ERROR]   at java.security.AccessController.doPrivileged(Native Method)
job-server[ERROR]   at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
job-server[ERROR]   at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
job-server[ERROR]   at java.lang.ClassLoader.loadClass(ClassLoader.java:358)

job-server[ERROR]   at      spark.jobserver.JobManagerActor$$anonfun$spark$jobserver$JobManagerActor$$getJobFuture$4.apply(JobMan    agerActor.scala:222)
job-server[ERROR]   at      scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
job-server[ERROR]   at     scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
job-server[ERROR]   at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:42)
job-server[ERROR]   at    akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:386)
job-server[ERROR]   at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
job-server[ERROR]   at    scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
job-server[ERROR]   at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
job-server[ERROR]   at     scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
job-server ... finished with exit code 255