add Java part for fault handling docs

akka-docs/java/code/akka/docs/actor/FaultHandlingTest.scala

@@ -0,0 +1,4 @@
+package akka.docs.actor
+import org.scalatest.junit.JUnitSuite
+
+class FaultHandlingTest extends FaultHandlingTestBase with JUnitSuite

akka-docs/java/code/akka/docs/actor/FaultHandlingTestBase.java

@@ -0,0 +1,167 @@
+package akka.docs.actor;
+
+//#testkit
+import akka.actor.ActorRef;
+import akka.actor.ActorSystem;
+import akka.actor.FaultHandlingStrategy;
+import static akka.actor.FaultHandlingStrategy.*;
+import akka.actor.OneForOneStrategy;
+import akka.actor.Props;
+import akka.actor.Terminated;
+import akka.actor.UntypedActor;
+import akka.dispatch.Await;
+import akka.util.Duration;
+import akka.testkit.AkkaSpec;
+import akka.testkit.TestProbe;
+
+//#testkit
+import akka.testkit.ErrorFilter;
+import akka.testkit.EventFilter;
+import akka.testkit.TestEvent;
+import static java.util.concurrent.TimeUnit.SECONDS;
+import akka.japi.Function;
+import scala.Option;
+import scala.collection.JavaConverters;
+import scala.collection.Seq;
+
+import org.junit.Test;
+import org.junit.BeforeClass;
+import org.junit.AfterClass;
+
+//#testkit
+public class FaultHandlingTestBase {
+  //#testkit
+  //#supervisor
+  static public class Supervisor extends UntypedActor {
+    public void onReceive(Object o) {
+      if (o instanceof Props) {
+        getSender().tell(getContext().actorOf((Props) o));
+      }
+    }
+  }
+  //#supervisor
+  
+  //#supervisor2
+  static public class Supervisor2 extends UntypedActor {
+    public void onReceive(Object o) {
+      if (o instanceof Props) {
+        getSender().tell(getContext().actorOf((Props) o));
+      }
+    }
+    
+    @Override
+    public void preRestart(Throwable cause, Option<Object> msg) {
+      // do not kill all children, which is the default here
+    }
+  }
+  //#supervisor2
+  
+  //#child
+  static public class Child extends UntypedActor {
+    int state = 0;
+    
+    public void onReceive(Object o) throws Exception {
+      if (o instanceof Exception) {
+        throw (Exception) o;
+      } else if (o instanceof Integer) {
+        state = (Integer) o;
+      } else if (o.equals("get")) {
+        getSender().tell(state);
+      }
+    }
+  }
+  //#child
+  
+  //#strategy
+  static FaultHandlingStrategy strategy = new OneForOneStrategy(new Function<Throwable, Action>() {
+    @Override
+    public Action apply(Throwable t) {
+      if (t instanceof ArithmeticException) {
+        return resume();
+      } else if (t instanceof NullPointerException) {
+        return restart();
+      } else if (t instanceof IllegalArgumentException) {
+        return stop();
+      } else {
+        return escalate();
+      }
+    }
+  }, 10, 60000);
+  //#strategy
+  
+  //#testkit
+  static ActorSystem system;
+  Duration timeout = Duration.create(5, SECONDS);
+  
+  @BeforeClass
+  public static void start() {
+    system = ActorSystem.create("test", AkkaSpec.testConf());
+  }
+  
+  @AfterClass
+  public static void cleanup() {
+    system.shutdown();
+  }
+  
+  @Test
+  public void mustEmployFaultHandler() {
+    // code here
+    //#testkit
+    EventFilter ex1 = (EventFilter) new ErrorFilter(ArithmeticException.class);
+    EventFilter ex2 = (EventFilter) new ErrorFilter(NullPointerException.class);
+    EventFilter ex3 = (EventFilter) new ErrorFilter(IllegalArgumentException.class);
+    EventFilter ex4 = (EventFilter) new ErrorFilter(Exception.class);
+    Seq<EventFilter> ignoreExceptions = seq(ex1, ex2, ex3, ex4);
+    system.eventStream().publish(new TestEvent.Mute(ignoreExceptions));
+    
+    //#create
+    Props superprops = new Props(Supervisor.class).withFaultHandler(strategy);
+    ActorRef supervisor = system.actorOf(superprops, "supervisor");
+    ActorRef child = (ActorRef) Await.result(supervisor.ask(new Props(Child.class), 5000), timeout);
+    //#create
+    
+    //#resume
+    child.tell(42);
+    assert Await.result(child.ask("get", 5000), timeout).equals(42);
+    child.tell(new ArithmeticException());
+    assert Await.result(child.ask("get", 5000), timeout).equals(42);
+    //#resume
+    
+    //#restart
+    child.tell(new NullPointerException());
+    assert Await.result(child.ask("get", 5000), timeout).equals(0);
+    //#restart
+    
+    //#stop
+    final TestProbe probe = new TestProbe(system);
+    probe.watch(child);
+    child.tell(new IllegalArgumentException());
+    probe.expectMsg(new Terminated(child));
+    //#stop
+    
+    //#escalate-kill
+    child = (ActorRef) Await.result(supervisor.ask(new Props(Child.class), 5000), timeout);
+    probe.watch(child);
+    assert Await.result(child.ask("get", 5000), timeout).equals(0);
+    child.tell(new Exception());
+    probe.expectMsg(new Terminated(child));
+    //#escalate-kill
+    
+    //#escalate-restart
+    superprops = new Props(Supervisor2.class).withFaultHandler(strategy);
+    supervisor = system.actorOf(superprops, "supervisor2");
+    child = (ActorRef) Await.result(supervisor.ask(new Props(Child.class), 5000), timeout);
+    child.tell(23);
+    assert Await.result(child.ask("get", 5000), timeout).equals(23);
+    child.tell(new Exception());
+    assert Await.result(child.ask("get", 5000), timeout).equals(0);
+    //#escalate-restart
+    //#testkit
+  }
+//#testkit
+  public <A> Seq<A> seq(A... args) {
+    return JavaConverters.collectionAsScalaIterableConverter(java.util.Arrays.asList(args)).asScala().toSeq();
+  }
+//#testkit
+}
+//#testkit

akka-docs/java/fault-tolerance.rst

@@ -1,10 +1,102 @@
 .. _fault-tolerance-java:
 
-Fault Tolerance Through Supervisor Hierarchies (Java)
-=====================================================
+Fault Handling Strategies (Java)
+=================================
 
 .. sidebar:: Contents
 
    .. contents:: :local:
 
-REWRITE ME
+As explained in :ref:`actor-systems` each actor is the supervisor of its
+children, and as such each actor is given a fault handling strategy when it is
+created. This strategy cannot be changed afterwards as it is an integral part
+of the actor system’s structure.
+
+Creating a Fault Handling Strategy
+----------------------------------
+
+For the sake of demonstration let us consider the following strategy:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: strategy
+
+I have chosen a few well-known exception types in order to demonstrate the
+application of the fault handling actions described in :ref:`supervision`.
+First off, it is a one-for-one strategy, meaning that each child is treated
+separately (an all-for-one strategy works very similarly, the only difference
+is that any decision is applied to all children of the supervisor, not only the
+failing one). There are limits set on the restart frequency, namely maximum 10
+restarts per minute; each of these settings defaults to could be left out, which means
+that the respective limit does not apply, leaving the possibility to specify an
+absolute upper limit on the restarts or to make the restarts work infinitely.
+
+Practical Application
+---------------------
+
+The following section shows the effects of the different actions in practice,
+wherefor a test setup is needed. First off, we need a suitable supervisor:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: supervisor
+
+This supervisor will be used to create a child, with which we can experiment:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: child
+
+The test is easier by using the utilities described in :ref:`akka-testkit`,
+where ``TestProbe`` provides an actor ref useful for receiving and inspecting replies.
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: testkit
+
+Using the strategy shown above let us create actors:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: create
+
+The first test shall demonstrate the ``Resume`` action, so we try it out by
+setting some non-initial state in the actor and have it fail:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: resume
+
+As you can see the value 42 survives the fault handling action. Now, if we
+change the failure to a more serious ``NullPointerException``, that will no
+longer be the case:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: restart
+
+And finally in case of the fatal ``IllegalArgumentException`` the child will be
+terminated by the supervisor:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: stop
+
+Up to now the supervisor was completely unaffected by the child’s failure,
+because the actions set did handle it. In case of an ``Exception``, this is not
+true anymore and the supervisor escalates the failure.
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: escalate-kill
+
+The supervisor itself is supervised by the top-level actor provided by the
+:class:`ActorSystem`, which has the default policy to restart in case of all
+``Exception`` cases (with the notable exceptions of
+``ActorInitializationException`` and ``ActorKilledException``). Since the
+default action in case of a restart is to kill all children, we expected our poor
+child not to survive this failure.
+
+In case this is not desired (which depends on the use case), we need to use a
+different supervisor which overrides this behavior.
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: supervisor2
+
+With this parent, the child survives the escalated restart, as demonstrated in
+the last test:
+
+.. includecode:: code/akka/docs/actor/FaultHandlingTestBase.java
+   :include: escalate-restart
+