pekko/akka-samples/akka-sample-persistence-java8/src/main/java/sample/persistence/SnapshotExample.java

/**
 * 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.AbstractProcessor;
import akka.persistence.Persistent;
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 ExampleProcessor extends AbstractProcessor {
        private ExampleState state = new ExampleState();

        @Override public PartialFunction<Object, BoxedUnit> receive() {
            return ReceiveBuilder.
                match(Persistent.class, p -> state.update(String.format("%s-%d", p.payload(), p.sequenceNr()))).
                match(SnapshotOffer.class, s -> {
                    ExampleState exState = (ExampleState) s.snapshot();
                    System.out.println("offered state = " + exState);
                    state = exState;
                }).
                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())).build();
        }
    }

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

        processor.tell(Persistent.create("a"), null);
        processor.tell(Persistent.create("b"), null);
        processor.tell("snap", null);
        processor.tell(Persistent.create("c"), null);
        processor.tell(Persistent.create("d"), null);
        processor.tell("print", null);

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