Deprecation of ExtensionKey #22208

akka-actor-tests/src/test/java/akka/actor/JavaExtension.java

@@ -33,9 +33,24 @@ public class JavaExtension extends JUnitSuite {
     }
   }
 
+  static class OtherExtensionId extends AbstractExtensionId<OtherExtension> implements ExtensionIdProvider {
+
+    public final static OtherExtensionId OtherExtensionProvider = new OtherExtensionId();
+
+    @Override
+    public ExtensionId<OtherExtension> lookup() {
+      return OtherExtensionId.OtherExtensionProvider;
+    }
+
+    @Override
+    public OtherExtension createExtension(ExtendedActorSystem system) {
+      return new OtherExtension(system);
+    }
+
+  }
+
   static class OtherExtension implements Extension {
-    static final ExtensionKey<OtherExtension> key = new ExtensionKey<OtherExtension>(OtherExtension.class) {
-    };
+    static final ExtensionId<OtherExtension> key = OtherExtensionId.OtherExtensionProvider;
 
     public final ExtendedActorSystem system;
 

akka-actor/src/main/scala/akka/actor/Extension.scala

@@ -61,8 +61,6 @@ import scala.reflect.ClassTag
  *    ...
  * }
  * }}}
- *
- * See also [[akka.actor.ExtensionKey]] for a concise way of formulating extensions.
  */
 trait Extension
 
@@ -146,6 +144,7 @@ trait ExtensionIdProvider {
  * `get` method.
  *
  */
+@deprecated(message = "Use a regular Extension instead", since = "2.5.0")
 abstract class ExtensionKey[T <: Extension](implicit m: ClassTag[T]) extends ExtensionId[T] with ExtensionIdProvider {
   def this(clazz: Class[T]) = this()(ClassTag(clazz))
 

akka-actor/src/main/scala/akka/event/Logging.scala

@@ -5,13 +5,12 @@ package akka.event
 
 import java.util.concurrent.TimeoutException
 import java.util.concurrent.atomic.AtomicInteger
-import java.util.logging
 
 import akka.actor.ActorSystem.Settings
 import akka.actor._
 import akka.dispatch.RequiresMessageQueue
-import akka.event.Logging.{ Extension ⇒ _, _ }
-import akka.util.{ OptionVal, ReentrantGuard }
+import akka.event.Logging._
+import akka.util.ReentrantGuard
 import akka.util.Helpers.toRootLowerCase
 import akka.{ AkkaException, ConfigurationException }
 
@@ -175,7 +174,7 @@ trait LoggingBus extends ActorEventBus {
    * INTERNAL API
    */
   private def addLogger(system: ActorSystemImpl, clazz: Class[_ <: Actor], level: LogLevel, logName: String): ActorRef = {
-    val name = "log" + Extension(system).id() + "-" + simpleName(clazz)
+    val name = "log" + LogExt(system).id() + "-" + simpleName(clazz)
     val actor = system.systemActorOf(Props(clazz).withDispatcher(system.settings.LoggersDispatcher), name)
     implicit def timeout = system.settings.LoggerStartTimeout
     import akka.pattern.ask
@@ -409,7 +408,10 @@ object Logging {
   /**
    * INTERNAL API
    */
-  private[akka] object Extension extends ExtensionKey[LogExt]
+  private[akka] object LogExt extends ExtensionId[LogExt] {
+    override def createExtension(system: ExtendedActorSystem): LogExt =
+      new LogExt(system)
+  }
 
   /**
    * INTERNAL API

akka-docs/rst/project/migration-guide-2.4.x-2.5.x.rst

@@ -216,6 +216,30 @@ Actor DSL deprecation
 Actor DSL is a rarely used feature and thus will be deprecated and removed.
 Use plain ``system.actorOf`` instead of the DSL to create Actors if you have been using it.
 
+ExtensionKey Deprecation
+------------------------
+
+``ExtensionKey`` is a shortcut for writing :ref:`extending-akka-scala` but extensions created with it
+cannot be used from Java and it does in fact not save many lines of code over directly implementing ``ExtensionId``.
+
+
+Old::
+
+  object MyExtension extends ExtensionKey[MyExtension]
+
+New::
+
+  object MyExtension extends extends ExtensionId[MyExtension] with ExtensionIdProvider {
+
+    override def lookup = MyExtension
+
+    override def createExtension(system: ExtendedActorSystem): MyExtension =
+      new MyExtension(system)
+
+    // needed to get the type right when used from Java
+    override def get(system: ActorSystem): MyExtension = super.get(system)
+  }
+
 Streams
 =======
 

akka-docs/rst/scala/code/docs/serialization/SerializationDocSpec.scala

@@ -4,6 +4,7 @@
 
 package docs.serialization {
 
+  import akka.actor.{ExtensionId, ExtensionIdProvider}
   import akka.testkit._
   //#imports
   import akka.actor.{ ActorRef, ActorSystem }
@@ -11,7 +12,6 @@ package docs.serialization {
   import com.typesafe.config.ConfigFactory
 
   //#imports
-  import akka.actor.ExtensionKey
   import akka.actor.ExtendedActorSystem
   import akka.actor.Extension
   import akka.actor.Address
@@ -218,7 +218,14 @@ package docs.serialization {
       //#actorref-serializer
 
       //#external-address
-      object ExternalAddress extends ExtensionKey[ExternalAddressExt]
+      object ExternalAddress extends ExtensionId[ExternalAddressExt] with ExtensionIdProvider {
+        override def lookup() = ExternalAddress
+
+        override def createExtension(system: ExtendedActorSystem): ExternalAddressExt =
+          new ExternalAddressExt(system)
+
+        override def get(system: ActorSystem): ExternalAddressExt = super.get(system)
+      }
 
       class ExternalAddressExt(system: ExtendedActorSystem) extends Extension {
         def addressFor(remoteAddr: Address): Address =
@@ -236,7 +243,14 @@ package docs.serialization {
       val theActorSystem: ActorSystem = system
 
       //#external-address-default
-      object ExternalAddress extends ExtensionKey[ExternalAddressExt]
+      object ExternalAddress extends ExtensionId[ExternalAddressExt] with ExtensionIdProvider {
+        override def lookup() = ExternalAddress
+
+        override def createExtension(system: ExtendedActorSystem): ExternalAddressExt =
+          new ExternalAddressExt(system)
+
+        override def get(system: ActorSystem): ExternalAddressExt = super.get(system)
+      }
 
       class ExternalAddressExt(system: ExtendedActorSystem) extends Extension {
         def addressForAkka: Address = system.provider.getDefaultAddress

akka-persistence/src/test/scala/akka/persistence/PersistentActorJournalProtocolSpec.scala

@@ -74,7 +74,14 @@ akka.persistence.snapshot-store.plugin = "akka.persistence.no-snapshot-store"
   }
 }
 
-object JournalPuppet extends ExtensionKey[JournalProbe]
+object JournalPuppet extends ExtensionId[JournalProbe] with ExtensionIdProvider {
+  override def lookup()= JournalPuppet
+
+  override def createExtension(system: ExtendedActorSystem): JournalProbe =
+    new JournalProbe()(system)
+
+  override def get(system: ActorSystem): JournalProbe = super.get(system)
+}
 class JournalProbe(implicit private val system: ExtendedActorSystem) extends Extension {
   val probe = TestProbe()
   val ref = probe.ref

project/MiMa.scala

@@ -433,7 +433,10 @@ object MiMa extends AutoPlugin {
       ProblemFilters.exclude[IncompatibleResultTypeProblem]("akka.cluster.ddata.DurableStore#Store.data"),
       ProblemFilters.exclude[IncompatibleMethTypeProblem]("akka.cluster.ddata.DurableStore#Store.copy"),
       ProblemFilters.exclude[IncompatibleMethTypeProblem]("akka.cluster.ddata.DurableStore#Store.this"),
-      ProblemFilters.exclude[IncompatibleMethTypeProblem]("akka.cluster.ddata.LmdbDurableStore.dbPut")
+      ProblemFilters.exclude[IncompatibleMethTypeProblem]("akka.cluster.ddata.LmdbDurableStore.dbPut"),
+
+      // #22208 remove extension key
+      ProblemFilters.exclude[MissingClassProblem]("akka.event.Logging$Extension$")
 
       // NOTE: filters that will be backported to 2.4 should go to the latest 2.4 version below
     )