+doc #17877 document filtering for subclasses in eventStream

akka-docs/rst/java/code/docs/event/LoggingDocTest.java

@@ -4,10 +4,7 @@
 package docs.event;
 
 //#imports
-import akka.actor.ActorRef;
-import akka.actor.ActorSystem;
-import akka.actor.AllDeadLetters;
-import akka.actor.SuppressedDeadLetter;
+import akka.actor.*;
 import akka.event.Logging;
 import akka.event.LoggingAdapter;
 
@@ -34,11 +31,8 @@ import java.util.Map;
 //#imports-mdc
 
 //#imports-deadletter
-import akka.actor.Props;
 import akka.actor.ActorRef;
 import akka.actor.ActorSystem;
-import akka.actor.UntypedActor;
-import akka.actor.DeadLetter;
 //#imports-deadletter
 
 public class LoggingDocTest {
@@ -69,6 +63,56 @@ public class LoggingDocTest {
     JavaTestKit.shutdownActorSystem(system);
   }
 
+  //#superclass-subscription-eventstream
+  interface AllKindsOfMusic { }
+
+  class Jazz implements AllKindsOfMusic {
+    final public String artist;
+    public Jazz(String artist) {
+      this.artist = artist;
+    }
+  }
+  class Electronic implements AllKindsOfMusic {
+    final public String artist;
+    public Electronic(String artist) {
+      this.artist = artist;
+    }
+  }
+
+  class Listener extends UntypedActor {
+    @Override
+    public void onReceive(Object message) throws Exception {
+      if (message instanceof Jazz) {
+        System.out.printf("%s is listening to: %s%n", self().path().name(), message);
+      } else if (message instanceof Electronic) {
+        System.out.printf("%s is listening to: %s%n", self().path().name(), message);
+      }
+    }
+  }
+  //#superclass-subscription-eventstream
+
+  @Test
+  public void subscribeBySubclassification() {
+    final ActorSystem system = ActorSystem.create("DeadLetters");
+    //#superclass-subscription-eventstream
+    final ActorRef actor = system.actorOf(Props.create(DeadLetterActor.class));
+    system.eventStream().subscribe(actor, DeadLetter.class);
+
+    final ActorRef jazzListener = system.actorOf(Props.create(Listener.class));
+    final ActorRef musicListener = system.actorOf(Props.create(Listener.class));
+    system.eventStream().subscribe(jazzListener, Jazz.class);
+    system.eventStream().subscribe(musicListener, AllKindsOfMusic.class);
+
+    // only musicListener gets this message, since it listens to *all* kinds of music:
+    system.eventStream().publish(new Electronic("Parov Stelar"));
+
+    // jazzListener and musicListener will be notified about Jazz:
+    system.eventStream().publish(new Jazz("Sonny Rollins"));
+
+    //#superclass-subscription-eventstream
+    JavaTestKit.shutdownActorSystem(system);
+  }
+
   @Test
   public void subscribeToSuppressedDeadLetters() {
     final ActorSystem system = ActorSystem.create("SuppressedDeadLetters");

akka-docs/rst/java/event-bus.rst

@@ -148,6 +148,12 @@ it can be subscribed like this:
 
 .. includecode:: code/docs/event/LoggingDocTest.java#deadletters
 
+It is also worth pointing out that thanks to the way the subchannel classification
+is implemented in the event stream, it is possible to subscribe to a group of events, by
+subscribing to their common superclass as demonstrated in the following example:
+
+.. includecode:: code/docs/event/LoggingDocTest.java#superclass-subscription-eventstream
+
 Similarly to `Actor Classification`_, :class:`EventStream` will automatically remove subscribers when they terminate.
 
 .. note::

akka-docs/rst/scala/code/docs/event/LoggingDocSpec.scala

@@ -3,10 +3,8 @@
  */
 package docs.event
 
-import akka.actor.AllDeadLetters
+import akka.actor.{ Actor, Props }
 import akka.testkit.AkkaSpec
-import akka.actor.Actor
-import akka.actor.Props
 
 object LoggingDocSpec {
 
@@ -77,12 +75,12 @@ object LoggingDocSpec {
   //#mdc-actor
 
   //#my-event-listener
+  import akka.event.Logging.Debug
+  import akka.event.Logging.Error
+  import akka.event.Logging.Info
   import akka.event.Logging.InitializeLogger
   import akka.event.Logging.LoggerInitialized
-  import akka.event.Logging.Error
   import akka.event.Logging.Warning
-  import akka.event.Logging.Info
-  import akka.event.Logging.Debug
 
   class MyEventListener extends Actor {
     def receive = {
@@ -96,8 +94,8 @@ object LoggingDocSpec {
   //#my-event-listener
 
   //#my-source
-  import akka.event.LogSource
   import akka.actor.ActorSystem
+  import akka.event.LogSource
 
   object MyType {
     implicit val logSource: LogSource[AnyRef] = new LogSource[AnyRef] {
@@ -113,11 +111,12 @@ object LoggingDocSpec {
     val log = Logging(system, this)
   }
   //#my-source
+
 }
 
 class LoggingDocSpec extends AkkaSpec {
 
-  import LoggingDocSpec.{ MyActor, MdcActor, MdcActorMixin, Req }
+  import LoggingDocSpec.{ MdcActor, MdcActorMixin, MyActor, Req }
 
   "use a logging actor" in {
     val myActor = system.actorOf(Props[MyActor])
@@ -144,12 +143,42 @@ class LoggingDocSpec extends AkkaSpec {
           case d: DeadLetter => println(d)
         }
       }
+
       val listener = system.actorOf(Props(classOf[Listener], this))
       system.eventStream.subscribe(listener, classOf[DeadLetter])
       //#deadletters
     }
   }
 
+  "demonstrate superclass subscriptions on eventStream" in {
+    def println(s: String) = ()
+    //#superclass-subscription-eventstream
+    abstract class AllKindsOfMusic { def artist: String }
+    case class Jazz(artist: String) extends AllKindsOfMusic
+    case class Electronic(artist: String) extends AllKindsOfMusic
+
+    new AnyRef {
+      class Listener extends Actor {
+        def receive = {
+          case m: Jazz       => println(s"${self.path.name} is listening to: ${m.artist}")
+          case m: Electronic => println(s"${self.path.name} is listening to: ${m.artist}")
+        }
+      }
+
+      val jazzListener = system.actorOf(Props(classOf[Listener], this))
+      val musicListener = system.actorOf(Props(classOf[Listener], this))
+      system.eventStream.subscribe(jazzListener, classOf[Jazz])
+      system.eventStream.subscribe(musicListener, classOf[AllKindsOfMusic])
+
+      // only musicListener gets this message, since it listens to *all* kinds of music:
+      system.eventStream.publish(Electronic("Parov Stelar"))
+
+      // jazzListener and musicListener will be notified about Jazz:
+      system.eventStream.publish(Jazz("Sonny Rollins"))
+      //#superclass-subscription-eventstream
+    }
+  }
+
   "allow registration to suppressed dead letters" in {
     new AnyRef {
       import akka.actor.Props

akka-docs/rst/scala/event-bus.rst

@@ -143,6 +143,12 @@ how a simple subscription works:
 
 .. includecode:: code/docs/event/LoggingDocSpec.scala#deadletters
 
+It is also worth pointing out that thanks to the way the subchannel classification
+is implemented in the event stream, it is possible to subscribe to a group of events, by
+subscribing to their common superclass as demonstrated in the following example:
+
+.. includecode:: code/docs/event/LoggingDocSpec.scala#superclass-subscription-eventstream
+
 Similarly to `Actor Classification`_, :class:`EventStream` will automatically remove subscribers when they terminate.
 
 .. note::