#22903 Fix code snippeds

* move scala and java sources out of paradox sources
* replace relative paths with $code$ and $akka$
* fix broken includes

akka-docs/src/main/java/jdocs/cluster/TransformationFrontend.java

@@ -0,0 +1,44 @@
+package jdocs.cluster;
+
+import static jdocs.cluster.TransformationMessages.BACKEND_REGISTRATION;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import jdocs.cluster.TransformationMessages.JobFailed;
+import jdocs.cluster.TransformationMessages.TransformationJob;
+import akka.actor.ActorRef;
+import akka.actor.Terminated;
+import akka.actor.AbstractActor;
+
+//#frontend
+public class TransformationFrontend extends AbstractActor {
+
+  List<ActorRef> backends = new ArrayList<ActorRef>();
+  int jobCounter = 0;
+
+  @Override
+  public Receive createReceive() {
+    return receiveBuilder()
+      .match(TransformationJob.class, job -> backends.isEmpty(), job -> {
+        getSender().tell(
+          new JobFailed("Service unavailable, try again later", job),
+            getSender());
+      })
+      .match(TransformationJob.class, job -> {
+        jobCounter++;
+        backends.get(jobCounter % backends.size())
+          .forward(job, getContext());
+      })
+      .matchEquals(BACKEND_REGISTRATION, x -> {
+        getContext().watch(getSender());
+        backends.add(getSender());
+      })
+      .match(Terminated.class, terminated -> {
+        backends.remove(terminated.getActor());
+      })
+      .build();
+  }
+
+}
+//#frontend