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/DependencyInjectionDocTest.java

@@ -0,0 +1,105 @@
+/**
+ * Copyright (C) 2009-2017 Lightbend Inc. <http://www.lightbend.com>
+ */
+package docs.actorlambda;
+
+import docs.AbstractJavaTest;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+import org.junit.Test;
+import scala.concurrent.Await;
+import scala.concurrent.duration.Duration;
+
+import akka.actor.AbstractActor;
+import akka.actor.ActorRef;
+import akka.actor.ActorSystem;
+import akka.actor.Props;
+import akka.testkit.JavaTestKit;
+
+//#import
+import akka.actor.Actor;
+import akka.actor.IndirectActorProducer;
+//#import
+
+public class DependencyInjectionDocTest extends AbstractJavaTest {
+
+  public static class TheActor extends AbstractActor {
+
+    final String s;
+    
+    public TheActor(String s) {
+      this.s = s;
+    }
+    
+    @Override
+    public Receive createReceive() {
+      return receiveBuilder()
+        .match(String.class, msg -> {
+          sender().tell(s, self());
+        })
+        .build();
+    }
+  }
+  
+  static ActorSystem system = null;
+
+  @BeforeClass
+  public static void beforeClass() {
+    system = ActorSystem.create("DependencyInjectionDocTest");
+  }
+
+  @AfterClass
+  public static void afterClass() throws Exception {
+    Await.ready(system.terminate(), Duration.create("5 seconds"));
+  }
+
+  //this is just to make the test below a tiny fraction nicer
+  private ActorSystem getContext() {
+    return system;
+  }
+  
+  static
+  //#creating-indirectly
+  class DependencyInjector implements IndirectActorProducer {
+    final Object applicationContext;
+    final String beanName;
+    
+    public DependencyInjector(Object applicationContext, String beanName) {
+      this.applicationContext = applicationContext;
+      this.beanName = beanName;
+    }
+    
+    @Override
+    public Class<? extends Actor> actorClass() {
+      return TheActor.class;
+    }
+    
+    @Override
+    public TheActor produce() {
+      TheActor result;
+      //#obtain-fresh-Actor-instance-from-DI-framework
+      result = new TheActor((String) applicationContext);
+      //#obtain-fresh-Actor-instance-from-DI-framework
+      return result;
+    }
+  }
+  //#creating-indirectly
+  
+  @Test
+  public void indirectActorOf() {
+    final String applicationContext = "...";
+    //#creating-indirectly
+    
+    final ActorRef myActor = getContext().actorOf(
+      Props.create(DependencyInjector.class, applicationContext, "TheActor"),
+        "TheActor");
+    //#creating-indirectly
+    new JavaTestKit(system) {
+      {
+        myActor.tell("hello", getRef());
+        expectMsgEquals("...");
+      }
+    };
+  }
+
+}