Akka/Scala example source code file (SnapshotExample.java)

This example Akka source code file (SnapshotExample.java) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Akka and Scala source code examples by using tags.

All credit for the original source code belongs to akka.io; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Akka tags/keywords

actor, actorsystem, akka, arraylist, examplestate, exception, japi, override, persistence, procedure, savesnapshotfailure, serializable, snapshotexample, string

The SnapshotExample.java Akka example source code

package sample.persistence;

import akka.actor.ActorRef;
import akka.actor.ActorSystem;
import akka.actor.Props;
import akka.japi.Procedure;
import akka.persistence.SaveSnapshotFailure;
import akka.persistence.SaveSnapshotSuccess;
import akka.persistence.SnapshotOffer;
import akka.persistence.UntypedPersistentActor;

import java.io.Serializable;
import java.util.ArrayList;

public class SnapshotExample {
    public static class ExampleState implements Serializable {
        private final ArrayList<String> received;

        public ExampleState() {
            this(new ArrayList<String>());
        }

        public ExampleState(ArrayList<String> received) {
            this.received = received;
        }

        public ExampleState copy() {
            return new ExampleState(new ArrayList<String>(received));
        }

        public void update(String s) {
            received.add(s);
        }

        @Override
        public String toString() {
            return received.toString();
        }
    }

    public static class ExamplePersistentActor extends UntypedPersistentActor {
        @Override
        public String persistenceId() { return "sample-id-3"; }

        private ExampleState state = new ExampleState();

        @Override
        public void onReceiveCommand(Object message) {
            if (message.equals("print")) {
                System.out.println("current state = " + state);
            } else if (message.equals("snap")) {
                // IMPORTANT: create a copy of snapshot
                // because ExampleState is mutable !!!
                saveSnapshot(state.copy());
            } else if (message instanceof SaveSnapshotSuccess) {
              // ...
            } else if (message instanceof SaveSnapshotFailure) {
              // ...  
            } else if (message instanceof String) {
              String s = (String) message;
              persist(s, new Procedure<String>() {
                public void apply(String evt) throws Exception {
                  state.update(evt);
                }
              });
            } else {
              unhandled(message);
            }
        }
        
        @Override
        public void onReceiveRecover(Object message) {
          if (message instanceof SnapshotOffer) {
            ExampleState s = (ExampleState)((SnapshotOffer)message).snapshot();
            System.out.println("offered state = " + s);
            state = s;
          } else if (message instanceof String) {
            state.update((String) message);
          } else {
            unhandled(message);
          }
        }

    }

    public static void main(String... args) throws Exception {
        final ActorSystem system = ActorSystem.create("example");
        final ActorRef persistentActor = system.actorOf(Props.create(ExamplePersistentActor.class), "persistentActor-3-java");

        persistentActor.tell("a", null);
        persistentActor.tell("b", null);
        persistentActor.tell("snap", null);
        persistentActor.tell("c", null);
        persistentActor.tell("d", null);
        persistentActor.tell("print", null);

        Thread.sleep(1000);
        system.shutdown();
    }
}