improve AbstractActor, #21717

* Receive class that wraps PartialFunction, to avoid
  scary scala types
* move AbstractActorContext to AbstractActor.ActorContext
* converting docs, many, many UntypedActor
* removing UntypedActor docs
* add unit test for ReceiveBuilder
* MiMa filters
* consistent use of getContext(), self(), sender()
* rename cross references
* migration guide
* skip samples for now
* improve match type safetyi, add matchUnchecked
  * the `? extends P` caused code like this to compile:
    `match(String.class, (Integer i) -> {})`
  * added matchUnchecked, since it can still be useful (um, convenient)
    to be able to do:
    `matchUnchecked(List.class, (List<String> list) -> {})`
* eleminate some scala.Option
  * preRestart
  * findChild
  * ActorIdentity.getActorRef

akka-docs/rst/java/code/docs/actorlambda/japi/FaultHandlingDocSample.java

@@ -67,24 +67,24 @@ public class FaultHandlingDocSample {
     public void preStart() {
       // If we don't get any progress within 15 seconds then the service
       // is unavailable
-      context().setReceiveTimeout(Duration.create("15 seconds"));
+      getContext().setReceiveTimeout(Duration.create("15 seconds"));
     }
 
-    public Listener() {
-      receive(LoggingReceive.create(ReceiveBuilder.
+    @Override
+    public Receive createReceive() {
+      return LoggingReceive.create(receiveBuilder().
         match(Progress.class, progress -> {
           log().info("Current progress: {} %", progress.percent);
           if (progress.percent >= 100.0) {
             log().info("That's all, shutting down");
-            context().system().terminate();
+            getContext().system().terminate();
           }
         }).
         matchEquals(ReceiveTimeout.getInstance(), x -> {
           // No progress within 15 seconds, ServiceUnavailable
           log().error("Shutting down due to unavailable service");
-          context().system().terminate();
-        }).build(), context()
-      ));
+          getContext().system().terminate();
+        }).build(), getContext());
     }
   }
 
@@ -119,7 +119,7 @@ public class FaultHandlingDocSample {
     // The sender of the initial Start message will continuously be notified
     // about progress
     ActorRef progressListener;
-    final ActorRef counterService = context().actorOf(
+    final ActorRef counterService = getContext().actorOf(
       Props.create(CounterService.class), "counter");
     final int totalCount = 51;
 
@@ -134,13 +134,14 @@ public class FaultHandlingDocSample {
       return strategy;
     }
 
-    public Worker() {
-      receive(LoggingReceive.create(ReceiveBuilder.
+    @Override
+    public Receive createReceive() {
+      return LoggingReceive.create(receiveBuilder().
         matchEquals(Start, x -> progressListener == null, x -> {
           progressListener = sender();
-          context().system().scheduler().schedule(
+          getContext().system().scheduler().schedule(
             Duration.Zero(), Duration.create(1, "second"), self(), Do,
-            context().dispatcher(), null
+            getContext().dispatcher(), null
           );
         }).
         matchEquals(Do, x -> {
@@ -154,10 +155,9 @@ public class FaultHandlingDocSample {
               public Progress apply(CurrentCount c) {
                 return new Progress(100.0 * c.count / totalCount);
               }
-            }, context().dispatcher()), context().dispatcher())
+            }, getContext().dispatcher()), getContext().dispatcher())
             .to(progressListener);
-        }).build(), context())
-      );
+        }).build(), getContext());
     }
   }
 
@@ -254,7 +254,7 @@ public class FaultHandlingDocSample {
      * when it has been terminated.
      */
     void initStorage() {
-      storage = context().watch(context().actorOf(
+      storage = getContext().watch(getContext().actorOf(
         Props.create(Storage.class), "storage"));
       // Tell the counter, if any, to use the new storage
       if (counter != null)
@@ -263,12 +263,13 @@ public class FaultHandlingDocSample {
       storage.tell(new Get(key), self());
     }
 
-    public CounterService() {
-      receive(LoggingReceive.create(ReceiveBuilder.
+    @Override
+    public Receive createReceive() {
+      return LoggingReceive.create(receiveBuilder().
         match(Entry.class, entry -> entry.key.equals(key) && counter == null, entry -> {
           // Reply from Storage of the initial value, now we can create the Counter
           final long value = entry.value;
-          counter = context().actorOf(Props.create(Counter.class, key, value));
+          counter = getContext().actorOf(Props.create(Counter.class, key, value));
           // Tell the counter to use current storage
           counter.tell(new UseStorage(storage), self());
           // and send the buffered backlog to the counter
@@ -290,15 +291,14 @@ public class FaultHandlingDocSample {
           // Tell the counter that there is no storage for the moment
           counter.tell(new UseStorage(null), self());
           // Try to re-establish storage after while
-          context().system().scheduler().scheduleOnce(
+          getContext().system().scheduler().scheduleOnce(
             Duration.create(10, "seconds"), self(), Reconnect,
-            context().dispatcher(), null);
+            getContext().dispatcher(), null);
         }).
         matchEquals(Reconnect, o -> {
           // Re-establish storage after the scheduled delay
           initStorage();
-        }).build(), context())
-      );
+        }).build(), getContext());
     }
 
     void forwardOrPlaceInBacklog(Object msg) {
@@ -311,7 +311,7 @@ public class FaultHandlingDocSample {
             " lack of initial value");
         backlog.add(new SenderMsgPair(sender(), msg));
       } else {
-        counter.forward(msg, context());
+        counter.forward(msg, getContext());
       }
     }
   }
@@ -345,8 +345,11 @@ public class FaultHandlingDocSample {
     public Counter(String key, long initialValue) {
       this.key = key;
       this.count = initialValue;
-
-      receive(LoggingReceive.create(ReceiveBuilder.
+    }
+    
+    @Override
+    public Receive createReceive() {
+      return LoggingReceive.create(receiveBuilder().
         match(UseStorage.class, useStorage -> {
           storage = useStorage.storage;
           storeCount();
@@ -357,8 +360,7 @@ public class FaultHandlingDocSample {
         }).
         matchEquals(GetCurrentCount, gcc -> {
           sender().tell(new CurrentCount(key, count), self());
-        }).build(), context())
-      );
+        }).build(), getContext());
     }
 
     void storeCount() {
@@ -430,8 +432,9 @@ public class FaultHandlingDocSample {
 
     final DummyDB db = DummyDB.instance;
 
-    public Storage() {
-      receive(LoggingReceive.create(ReceiveBuilder.
+    @Override
+    public Receive createReceive() {
+      return LoggingReceive.create(receiveBuilder().
         match(Store.class, store -> {
           db.save(store.entry.key, store.entry.value);
         }).
@@ -439,8 +442,7 @@ public class FaultHandlingDocSample {
           Long value = db.load(get.key);
           sender().tell(new Entry(get.key, value == null ?
             Long.valueOf(0L) : value), self());
-        }).build(), context())
-      );
+        }).build(), getContext());
     }
   }