Remove samples (#22288)

Add code, that was used for documentation to the appropriate projects
or akka-docs.

akka-docs/rst/java/code/docs/cluster/TransformationBackend.java

@@ -0,0 +1,60 @@
+package docs.cluster;
+
+import static docs.cluster.TransformationMessages.BACKEND_REGISTRATION;
+import docs.cluster.TransformationMessages.TransformationJob;
+import docs.cluster.TransformationMessages.TransformationResult;
+import akka.actor.UntypedActor;
+import akka.cluster.Cluster;
+import akka.cluster.ClusterEvent.CurrentClusterState;
+import akka.cluster.ClusterEvent.MemberUp;
+import akka.cluster.Member;
+import akka.cluster.MemberStatus;
+
+//#backend
+public class TransformationBackend extends UntypedActor {
+
+  Cluster cluster = Cluster.get(getContext().system());
+
+  //subscribe to cluster changes, MemberUp
+  @Override
+  public void preStart() {
+    cluster.subscribe(getSelf(), MemberUp.class);
+  }
+
+  //re-subscribe when restart
+  @Override
+  public void postStop() {
+    cluster.unsubscribe(getSelf());
+  }
+
+  @Override
+  public void onReceive(Object message) {
+    if (message instanceof TransformationJob) {
+      TransformationJob job = (TransformationJob) message;
+      getSender().tell(new TransformationResult(job.getText().toUpperCase()),
+          getSelf());
+
+    } else if (message instanceof CurrentClusterState) {
+      CurrentClusterState state = (CurrentClusterState) message;
+      for (Member member : state.getMembers()) {
+        if (member.status().equals(MemberStatus.up())) {
+          register(member);
+        }
+      }
+
+    } else if (message instanceof MemberUp) {
+      MemberUp mUp = (MemberUp) message;
+      register(mUp.member());
+
+    } else {
+      unhandled(message);
+    }
+  }
+
+  void register(Member member) {
+    if (member.hasRole("frontend"))
+      getContext().actorSelection(member.address() + "/user/frontend").tell(
+          BACKEND_REGISTRATION, getSelf());
+  }
+}
+//#backend