!per #3704 Persistence improvements

- Channel enhancements (#3773):
- Live read models (#3776):
- Batch-oriented journal plugin API (#3804):
- Batching of confirmations and deletions
- Message deletion enhancements (more efficient range deletions)

akka-samples/akka-sample-persistence/src/main/java/sample/persistence/japi/ViewExample.java

@@ -0,0 +1,90 @@
+package sample.persistence.japi;
+
+import java.util.Scanner;
+
+import akka.actor.*;
+import akka.persistence.*;
+
+public class ViewExample {
+    public static class ExampleProcessor extends UntypedProcessor {
+        @Override
+        public String processorId() {
+            return "processor-5";
+        }
+
+        @Override
+        public void onReceive(Object message) throws Exception {
+            if (message instanceof Persistent) {
+                Persistent p = (Persistent)message;
+                System.out.println(String.format("processor received %s (sequence nr = %d)", p.payload(), p.sequenceNr()));
+            }
+        }
+    }
+
+    public static class ExampleView extends UntypedView {
+        private final ActorRef destination = getContext().actorOf(Props.create(ExampleDestination.class));
+        private final ActorRef channel = getContext().actorOf(Channel.props("channel"));
+
+        private int numReplicated = 0;
+
+        @Override
+        public String viewId() {
+            return "view-5";
+        }
+
+        @Override
+        public String processorId() {
+            return "processor-5";
+        }
+
+        @Override
+        public void onReceive(Object message) throws Exception {
+            if (message instanceof Persistent) {
+                Persistent p = (Persistent)message;
+                numReplicated += 1;
+                System.out.println(String.format("view received %s (sequence nr = %d, num replicated = %d)", p.payload(), p.sequenceNr(), numReplicated));
+                channel.tell(Deliver.create(p.withPayload("replicated-" + p.payload()), destination.path()), getSelf());
+            } else if (message instanceof SnapshotOffer) {
+                SnapshotOffer so = (SnapshotOffer)message;
+                numReplicated = (Integer)so.snapshot();
+                System.out.println(String.format("view received snapshot offer %s (metadata = %s)", numReplicated, so.metadata()));
+            } else if (message.equals("snap")) {
+                saveSnapshot(numReplicated);
+            }
+        }
+    }
+
+    public static class ExampleDestination extends UntypedActor {
+        @Override
+        public void onReceive(Object message) throws Exception {
+            if (message instanceof ConfirmablePersistent) {
+                ConfirmablePersistent cp = (ConfirmablePersistent)message;
+                System.out.println(String.format("destination received %s (sequence nr = %s)", cp.payload(), cp.sequenceNr()));
+                cp.confirm();
+            }
+        }
+    }
+
+    public static void main(String... args) throws Exception {
+        final ActorSystem system = ActorSystem.create("example");
+        final ActorRef processor = system.actorOf(Props.create(ExampleProcessor.class));
+        final ActorRef view = system.actorOf(Props.create(ExampleView.class));
+
+        Scanner scanner = new Scanner(System.in);
+
+        while (scanner.hasNextLine()) {
+            String line = scanner.nextLine();
+            if (line.equals("exit")) {
+                break;
+            } else if (line.equals("sync")) {
+                view.tell(Update.create(false), null);
+            } else if (line.equals("snap")) {
+                view.tell("snap", null);
+            } else {
+                processor.tell(Persistent.create(line), null);
+            }
+        }
+
+        system.shutdown();
+    }
+}