3fd240384c
A PersistentView works the same way as View did previously, except: * it requires an `peristenceId` (no default is provided) * messages given to `receive` are NOT wrapped in Persistent() akka-streams not touched, will update them afterwards on different branch Also solves #15436 by making persistentId in PersistentView abstract. (cherry picked from commit dcafaf788236fe6d018388dd55d5bf9650ded696) Conflicts: akka-docs/rst/java/lambda-persistence.rst akka-docs/rst/java/persistence.rst akka-docs/rst/scala/persistence.rst akka-persistence/src/main/scala/akka/persistence/Persistent.scala akka-persistence/src/main/scala/akka/persistence/View.scala
114 lines
4.7 KiB
HTML
114 lines
4.7 KiB
HTML
<!-- <html> -->
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<head>
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<title>Akka Persistence Samples in Java</title>
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</head>
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<body>
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<div>
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<h2>Akka Persistence Samples</h2>
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<p>
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This tutorial contains examples that illustrate a subset of
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<a href="http://doc.akka.io/docs/akka/2.4-SNAPSHOT/java/persistence.html" target="_blank">Akka Persistence</a> features.
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</p>
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<ul>
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<li>persistent actor</li>
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<li>persistent actor snapshots</li>
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<li>persistent actor recovery</li>
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<li>persistent actor views</li>
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</ul>
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<p>
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Custom storage locations for the journal and snapshots can be defined in
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<a href="#code/src/main/resources/application.conf" class="shortcut">application.conf</a>.
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</p>
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</div>
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<div>
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<h2>Persistent actor</h2>
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<p>
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<a href="#code/src/main/java/sample/persistence/PersistentActorExample.java" class="shortcut">PersistentActorExample.java</a>
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is described in detail in the <a href="http://doc.akka.io/docs/akka/2.3-SNAPSHOT/java/persistence.html#event-sourcing-java" target="_blank">Event sourcing</a>
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section of the user documentation. With every application run, the <code>ExamplePersistentActor</code> is recovered from
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events stored in previous application runs, processes new commands, stores new events and snapshots and prints the
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current persistent actor state to <code>stdout</code>.
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</p>
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<p>
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To run this example, go to the <a href="#run" class="shortcut">Run</a> tab, and run the application main class
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<b><code>sample.persistence.PersistentActorExample</code></b> several times.
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</p>
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</div>
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<div>
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<h2>Persistent actor snapshots</h2>
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<p>
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<a href="#code/src/main/java/sample/persistence/SnapshotExample.java" class="shortcut">SnapshotExample.java</a>
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demonstrates how persistent actors can take snapshots of application state and recover from previously stored snapshots.
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Snapshots are offered to persistent actors at the beginning of recovery, before any messages (younger than the snapshot)
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are replayed.
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</p>
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<p>
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To run this example, go to the <a href="#run" class="shortcut">Run</a> tab, and run the application main class
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<b><code>sample.persistence.SnapshotExample</code></b> several times. With every run, the state offered by the
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most recent snapshot is printed to <code>stdout</code>, followed by the updated state after sending new persistent
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messages to the persistent actor.
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</p>
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</div>
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<div>
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<h2>Persistent actor recovery</h2>
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<p>
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<a href="#code/src/main/java/sample/persistence/PersistentActorFailureExample.java" class="shortcut">PersistentActorFailureExample.java</a>
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shows how a persistent actor can throw an exception, restart and restore the state by replaying the events.
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</p>
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<p>
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To run this example, go to the <a href="#run" class="shortcut">Run</a> tab, and run the application main class
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<b><code>sample.persistence.PersistentActorFailureExample</code></b> several times.
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</p>
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</div>
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<div>
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<h2>Persistent actor views</h2>
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<p>
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<a href="#code/src/main/java/sample/persistence/ProcessorFailureExample.java" class="shortcut">ProcessorFailureExample.java</a>
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shows how a processor can delete persistent messages from the journal if they threw an exception. Throwing an exception
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restarts the processor and replays messages. In order to prevent that the message that caused the exception is replayed,
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it is marked as deleted in the journal (during invocation of <code>preRestart</code>). This is a common pattern in
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command-sourcing to compensate write-ahead logging of messages.
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</p>
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<p>
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To run this example, go to the <a href="#run" class="shortcut">Run</a> tab, and run the application main class
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<b><code>sample.persistence.ProcessorFailureExample</code></b> several times.
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</p>
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<p>
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<a href="http://doc.akka.io/docs/akka/2.4-SNAPSHOT/java/persistence.html#event-sourcing" target="_blank">Event sourcing</a>
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on the other hand, does not persist commands directly but rather events that have been derived from received commands
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(not shown here). These events are known to be successfully applicable to current processor state i.e. there's
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no need for deleting them from the journal. Event sourced processors usually have a lower throughput than command
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sourced processors, as the maximum size of a write batch is limited by the number of persisted events per received
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command.
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</p>
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</div>
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<div>
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<h2>Processor views</h2>
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<p>
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<a href="#code/src/main/java/sample/persistence/ViewExample.java" class="shortcut">ViewExample.java</a> demonstrates
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how a view (<code>ExampleView</code>) is updated with the persistent message stream of a persistent actor
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(<code>ExamplePersistentActor</code>). Messages sent to the persistent actor are scheduled periodically. Views also support
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snapshotting to reduce recovery time.
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</p>
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<p>
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To run this example, go to the <a href="#run" class="shortcut">Run</a> tab, and run the application main class
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<b><code>sample.persistence.PersistentViewExample</code></b>.
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</p>
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</div>
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</body>
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</html>
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