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

abstractpersistentactor, actor, actorsystem, akka, arraylist, boxedunit, examplestate, japi, override, partialfunction, persistence, receivebuilder, runtime, serializable, string

The SnapshotExample.java Akka example source code

/**
 * Copyright (C) 2009-2014 Typesafe Inc. <http://www.typesafe.com>
 */

package sample.persistence;

import akka.actor.ActorRef;
import akka.actor.ActorSystem;
import akka.actor.Props;
import akka.japi.pf.ReceiveBuilder;
import akka.persistence.AbstractPersistentActor;
import akka.persistence.SnapshotOffer;
import scala.PartialFunction;
import scala.runtime.BoxedUnit;

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 AbstractPersistentActor {
    private ExampleState state = new ExampleState();

    @Override
    public PartialFunction<Object, BoxedUnit> receiveCommand() {
      return ReceiveBuilder.
        match(String.class, s -> s.equals("print"), s -> System.out.println("current state = " + state)).
        match(String.class, s -> s.equals("snap"), s ->
          // IMPORTANT: create a copy of snapshot
          // because ExampleState is mutable !!!
          saveSnapshot(state.copy())).
        match(String.class, s -> {
          persist(s, evt -> {
            state.update(evt);
          });
        }).
        build();
    }

    @Override
    public String persistenceId() { return "sample-id-3"; }

    @Override
    public PartialFunction<Object, BoxedUnit> receiveRecover() {
      return ReceiveBuilder.
        match(String.class, evt -> state.update(evt)).
        match(SnapshotOffer.class, ss -> {
          System.out.println("offered state = " + ss);
          state = (ExampleState) ss.snapshot();
        }).
        build();
    }
  }

  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();
  }
}