akka学习教程(十一) akka持久化

akka系列文章目录

• akka学习教程(十四) akka分布式实战
• akka学习教程(十三) akka分布式
• akka学习教程(十二) Spring与Akka的集成
• akka学习教程(十一) akka持久化
• akka学习教程(十) agent
• akka学习教程(九) STM软件事务内存
• akka学习教程(八) Actor中的Future-询问模式
• akka学习教程(七) 内置状态转换Procedure
• akka学习教程(六) 路由器Router
• akka学习教程(五) inbox消息收件箱
• akka学习教程(四) actor生命周期
• akka学习教程(三) 不可变对象
• akka学习教程(二)HelloWord
• akka学习教程(一)简介

本文内容来自于官网文档示例: AKKA Persistence

Akka持久化简介

Akka持久化可以使有状态的actor能够保持其内部状态，以便在启动、JVM崩溃后重新启动、或在集群中迁移时，恢复它们的内部状态。 Akka持久性关键点在于，只有对actor内部状态的更改才会被持久化，而不会直接保持其当前状态（可选快照除外）。 这些更改只会追加到存储，没有任何修改，这允许非常高的事务速率和高效的复制。 通过加载持久化的数据Stateful actors可以重建内部状态。 这可以是所有修改的完整历史记录，也可以从一个快照开始，这可以显着减少恢复时间。 Akka持久性还提供至少一次消息传递语义的点对点通信。【翻译与官方文档】

接下来将官方文档的示例运行一遍

依赖与配置

引入persistence依赖

<dependency>    <groupId>com.typesafe.akka</groupId>    <artifactId>akka-persistence_2.11</artifactId>    <version>2.4.16</version></dependency>

Akka持久性扩展依赖一些内置持久性插件，包括基于内存堆的日志，基于本地文件系统的快照存储和基于LevelDB的日志。

基于LevelDB的插件将需要以下附加的依赖声明：

<dependency>  <groupId>org.iq80.leveldb</groupId>  <artifactId>leveldb</artifactId>  <version>0.7</version></dependency><dependency>  <groupId>org.fusesource.leveldbjni</groupId>  <artifactId>leveldbjni-all</artifactId>  <version>1.8</version></dependency>

不过本文没有使用leveldb。

添加配置文件

这里需要配置持久化使用到的配置信息journal

• 默认情况下，持久化actor或视图将使用在reference.conf配置资源的以下部分中配置的“default”日志和快照存储插件。
• 注意，在这种情况下，actor或视图只覆盖persistenceId方法。
• 当持久化actor或视图覆盖journalPluginId和snapshotPluginId方法时，actor或视图将由这些特定的持久性插件提供服务，而不是默认值。

reference.conf：

akka {  loglevel = "INFO"}akka.persistence.journal.plugin = "akka.persistence.journal.inmem"# Absolute path to the default snapshot store plugin configuration entry.akka.persistence.snapshot-store.plugin = "akka.persistence.snapshot-store.local"

上代码

package akka.serializable;import akka.actor.UntypedActor;import akka.event.Logging;import akka.event.LoggingAdapter;import akka.persistence.SnapshotOffer;import akka.persistence.UntypedPersistentActor;import com.alibaba.fastjson.JSON;import java.io.Serializable;import java.util.ArrayList;import java.util.UUID;import static java.util.Arrays.asList;class Cmd implements Serializable {    private static final long serialVersionUID = 1L;    private final String data;    public Cmd(String data) {        this.data = data;    }    public String getData() {        return data;    }}class Evt implements Serializable {    private static final long serialVersionUID = 1L;    private final String data;    private final String uuid;    public Evt(String data, String uuid) {        this.data = data;        this.uuid = uuid;    }    public String getUuid() {        return uuid;    }    public String getData() {        return data;    }}class ExampleState implements Serializable {    private static final long serialVersionUID = 1L;    private final ArrayList<String> events;    public ExampleState() {        this(new ArrayList<String>());    }    public ExampleState(ArrayList<String> events) {        this.events = events;    }    public ExampleState copy() {        return new ExampleState(new ArrayList<String>(events));    }    public void update(Evt evt) {        events.add(evt.getData());    }    public int size() {        return events.size();    }    @Override    public String toString() {        return events.toString();    }}class ExamplePersistentActor extends UntypedPersistentActor {    LoggingAdapter log = Logging.getLogger(getContext().system (), this );    @Override    public String persistenceId() { return "sample-id-1"; }    private ExampleState state = new ExampleState();    public int getNumEvents() {        return state.size();    }    /**     * Called on restart. Loads from Snapshot first, and then replays Journal Events to update state.     * @param msg     */    @Override    public void onReceiveRecover(Object msg) {        log.info("onReceiveRecover: " + JSON.toJSONString(msg));        if (msg instanceof Evt) {            log.info("onReceiveRecover -- msg instanceof Event");            log.info("event --- " + ((Evt) msg).getData());            state.update((Evt) msg);        } else if (msg instanceof SnapshotOffer) {            log.info("onReceiveRecover -- msg instanceof SnapshotOffer");            state = (ExampleState)((SnapshotOffer)msg).snapshot();        } else {          unhandled(msg);        }    }    /**     * Called on Command dispatch     * @param msg     */    @Override    public void onReceiveCommand(Object msg) {        log.info("onReceiveCommand: " + JSON.toJSONString(msg));        if (msg instanceof Cmd) {            final String data = ((Cmd)msg).getData();            // generate an event we will persist after being enriched with a uuid            final Evt evt1 = new Evt(data + "-" + getNumEvents(), UUID.randomUUID().toString());            final Evt evt2 = new Evt(data + "-" + (getNumEvents() + 1), UUID.randomUUID().toString());            // persist event and THEN update the state of the processor            persistAll(asList(evt1, evt2), evt -> {                state.update(evt);                if (evt.equals(evt2)) {                    // broadcast event on eventstream 发布该事件                    getContext().system().eventStream().publish(evt);                }            });        } else if (msg.equals("snap")) {            // IMPORTANT: create a copy of snapshot            // because ExampleState is mutable !!!            saveSnapshot(state.copy());        } else if (msg.equals("print")) {            System.out.println("state:  " + state);        } else {          unhandled(msg);        }    }}class EventHandler extends UntypedActor {    LoggingAdapter log = Logging.getLogger(getContext().system(), this);    @Override    public void onReceive(Object msg ) throws Exception {        log.info( "Handled Event: " + JSON.toJSONString(msg));    }}

main方法

package akka.serializable;import org.slf4j.Logger;import org.slf4j.LoggerFactory;import akka.actor.ActorRef;import akka.actor.ActorSystem;import akka.actor.Props;public class MainTest {  public static final Logger log = LoggerFactory.getLogger(System.class);  public static void main(String... args) throws Exception {    final ActorSystem actorSystem = ActorSystem.create("actor-server");    final ActorRef handler = actorSystem.actorOf(Props.create(EventHandler. class));    // 订阅    actorSystem.eventStream().subscribe(handler , Evt.class);    Thread.sleep(5000);    final ActorRef actorRef = actorSystem.actorOf(Props.create(ExamplePersistentActor. class), "eventsourcing-processor" );    actorRef.tell( new Cmd("CMD 1" ), null);    actorRef.tell( new Cmd("CMD 2" ), null);    actorRef.tell( new Cmd("CMD 3" ), null);    actorRef.tell( "snap", null );//发送保存快照命令    actorRef.tell( new Cmd("CMD 4" ), null);    actorRef.tell( new Cmd("CMD 5" ), null);    actorRef.tell( "print", null );    Thread.sleep(5000);    log.info( "Actor System Shutdown Starting..." );    actorSystem.shutdown();  }}

运行结果：

[INFO] [01/17/2017 16:16:02.526] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/eventsourcing-processor] onReceiveRecover: {}[INFO] [01/17/2017 16:16:02.526] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/eventsourcing-processor] onReceiveRecover -- msg instanceof SnapshotOffer[INFO] [01/17/2017 16:16:02.560] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/eventsourcing-processor] onReceiveRecover: {"instance":{"$ref":"@"}}[INFO] [01/17/2017 16:16:02.565] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: {"data":"CMD 1"}[INFO] [01/17/2017 16:16:02.591] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: {"data":"CMD 2"}[INFO] [01/17/2017 16:16:02.592] [actor-server-akka.actor.default-dispatcher-6] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: {"data":"CMD 3"}[INFO] [01/17/2017 16:16:02.593] [actor-server-akka.actor.default-dispatcher-8] [akka://actor-server/user/$a] Handled Event: {"data":"CMD 1-37","uuid":"fe0fca08-a415-425d-b618-c730b117ca7d"}[INFO] [01/17/2017 16:16:02.594] [actor-server-akka.actor.default-dispatcher-6] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: "snap"[INFO] [01/17/2017 16:16:02.595] [actor-server-akka.actor.default-dispatcher-8] [akka://actor-server/user/$a] Handled Event: {"data":"CMD 2-39","uuid":"76fbf9e8-befd-40f4-a4fe-49b5698c7c7d"}[INFO] [01/17/2017 16:16:02.595] [actor-server-akka.actor.default-dispatcher-8] [akka://actor-server/user/$a] Handled Event: {"data":"CMD 3-41","uuid":"3b9f70c2-83c5-47d3-9f0a-4710905c3cfe"}[INFO] [01/17/2017 16:16:02.595] [actor-server-akka.actor.default-dispatcher-6] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: {"data":"CMD 4"}[INFO] [01/17/2017 16:16:02.596] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/$a] Handled Event: {"data":"CMD 4-43","uuid":"f8bb1e7e-716e-4f3c-9d81-e4570e0501c0"}[INFO] [01/17/2017 16:16:02.596] [actor-server-akka.actor.default-dispatcher-8] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: {"data":"CMD 5"}[INFO] [01/17/2017 16:16:02.597] [actor-server-akka.actor.default-dispatcher-5] [akka://actor-server/user/$a] Handled Event: {"data":"CMD 5-45","uuid":"574f9cdf-59f3-421c-8337-df8a50c95ee6"}state:  [CMD 1-0, CMD 1-1, CMD 2-2, CMD 2-3, CMD 3-4, CMD 3-5, CMD 1-6, CMD 1-7, CMD 2-8, CMD 2-9, CMD 3-10, CMD 3-11, CMD 1-12, CMD 1-13, CMD 2-14, CMD 2-15, CMD 3-16, CMD 3-17, CMD 1-18, CMD 1-19, CMD 2-20, CMD 2-21, CMD 3-22, CMD 3-23, CMD 1-24, CMD 1-25, CMD 2-26, CMD 2-27, CMD 3-28, CMD 3-29, CMD 1-30, CMD 1-31, CMD 2-32, CMD 2-33, CMD 3-34, CMD 3-35, CMD 1-36, CMD 1-37, CMD 2-38, CMD 2-39, CMD 3-40, CMD 3-41, CMD 4-42, CMD 4-43, CMD 5-44, CMD 5-45][INFO] [01/17/2017 16:16:02.598] [actor-server-akka.actor.default-dispatcher-8] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: "print"[INFO] [01/17/2017 16:16:02.613] [actor-server-akka.actor.default-dispatcher-15] [akka://actor-server/user/eventsourcing-processor] onReceiveCommand: {}2017-01-17 16:16:06.835 [main            ] INFO  System                  - Actor System Shutdown Starting...Process finished with exit code 0

这里注意：如果再次执行该程序，系统会首先恢复上次处理器的状态。本程序中会首先恢复快照中的状态然后是其他的状态。
快照使得处理器的状态持久化更加高效。

假如现在运行结果是酱紫的：state:  [CMD 1-0, CMD 1-1, CMD 2-2, CMD 2-3, CMD 3-4, CMD 3-5, CMD 1-6, CMD 1-7, CMD 2-8, CMD 2-9, CMD 3-10, CMD 3-11, CMD 4-12, CMD 4-13, CMD 5-14, CMD 5-15]在运行一次，结果就是酱紫的：state:  [CMD 1-0, CMD 1-1, CMD 2-2, CMD 2-3, CMD 3-4, CMD 3-5, CMD 1-6, CMD 1-7, CMD 2-8, CMD 2-9, CMD 3-10, CMD 3-11, CMD 1-12, CMD 1-13, CMD 2-14, CMD 2-15, CMD 3-16, CMD 3-17, CMD 4-18, CMD 4-19, CMD 5-20, CMD 5-21]

由于我们采用的是默认的持久化策略，会持久化到本地磁盘，进入项目统计目录下，会看到文件夹snapshots:

参考资料

• 书籍《java高并发程序设计》
• AKKA官方文档