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Akka/Scala example source code file (serialization.rst)
The serialization.rst Akka example source code.. _serialization-java: ##################### Serialization ##################### Akka has a built-in Extension for serialization, and it is both possible to use the built-in serializers and to write your own. The serialization mechanism is both used by Akka internally to serialize messages, and available for ad-hoc serialization of whatever you might need it for. Usage ===== Configuration ------------- For Akka to know which ``Serializer`` to use for what, you need edit your :ref:`configuration`, in the "akka.actor.serializers"-section you bind names to implementations of the ``akka.serialization.Serializer`` you wish to use, like this: .. includecode:: ../scala/code/docs/serialization/SerializationDocSpec.scala#serialize-serializers-config After you've bound names to different implementations of ``Serializer`` you need to wire which classes should be serialized using which ``Serializer``, this is done in the "akka.actor.serialization-bindings"-section: .. includecode:: ../scala/code/docs/serialization/SerializationDocSpec.scala#serialization-bindings-config You only need to specify the name of an interface or abstract base class of the messages. In case of ambiguity, i.e. the message implements several of the configured classes, the most specific configured class will be used, i.e. the one of which all other candidates are superclasses. If this condition cannot be met, because e.g. ``java.io.Serializable`` and ``MyOwnSerializable`` both apply and neither is a subtype of the other, a warning will be issued. Akka provides serializers for :class:`java.io.Serializable` and `protobuf <http://code.google.com/p/protobuf/>`_ :class:`com.google.protobuf.GeneratedMessage` by default (the latter only if depending on the akka-remote module), so normally you don't need to add configuration for that; since :class:`com.google.protobuf.GeneratedMessage` implements :class:`java.io.Serializable`, protobuf messages will always by serialized using the protobuf protocol unless specifically overridden. In order to disable a default serializer, map its marker type to “none”:: akka.actor.serialization-bindings { "java.io.Serializable" = none } Verification ------------ If you want to verify that your messages are serializable you can enable the following config option: .. includecode:: ../scala/code/docs/serialization/SerializationDocSpec.scala#serialize-messages-config .. warning:: We only recommend using the config option turned on when you're running tests. It is completely pointless to have it turned on in other scenarios. If you want to verify that your ``Props`` are serializable you can enable the following config option: .. includecode:: ../scala/code/docs/serialization/SerializationDocSpec.scala#serialize-creators-config .. warning:: We only recommend using the config option turned on when you're running tests. It is completely pointless to have it turned on in other scenarios. Programmatic ------------ If you want to programmatically serialize/deserialize using Akka Serialization, here's some examples: .. includecode:: code/docs/serialization/SerializationDocTest.java :include: imports .. includecode:: code/docs/serialization/SerializationDocTest.java :include: programmatic For more information, have a look at the ``ScalaDoc`` for ``akka.serialization._`` Customization ============= So, lets say that you want to create your own ``Serializer``, you saw the ``docs.serialization.MyOwnSerializer`` in the config example above? Creating new Serializers ------------------------ First you need to create a class definition of your ``Serializer``, which is done by extending ``akka.serialization.JSerializer``, like this: .. includecode:: code/docs/serialization/SerializationDocTest.java :include: imports .. includecode:: code/docs/serialization/SerializationDocTest.java :include: my-own-serializer :exclude: ... Then you only need to fill in the blanks, bind it to a name in your :ref:`configuration` and then list which classes that should be serialized using it. Serializing ActorRefs --------------------- All ActorRefs are serializable using JavaSerializer, but in case you are writing your own serializer, you might want to know how to serialize and deserialize them properly. In the general case, the local address to be used depends on the type of remote address which shall be the recipient of the serialized information. Use :meth:`Serialization.serializedActorPath(actorRef)` like this: .. includecode:: code/docs/serialization/SerializationDocTest.java :include: imports .. includecode:: code/docs/serialization/SerializationDocTest.java :include: actorref-serializer This assumes that serialization happens in the context of sending a message through the remote transport. There are other uses of serialization, though, e.g. storing actor references outside of an actor application (database, etc.). In this case, it is important to keep in mind that the address part of an actor’s path determines how that actor is communicated with. Storing a local actor path might be the right choice if the retrieval happens in the same logical context, but it is not enough when deserializing it on a different network host: for that it would need to include the system’s remote transport address. An actor system is not limited to having just one remote transport per se, which makes this question a bit more interesting. To find out the appropriate address to use when sending to ``remoteAddr`` you can use :meth:`ActorRefProvider.getExternalAddressFor(remoteAddr)` like this: .. includecode:: code/docs/serialization/SerializationDocTest.java :include: external-address .. note:: ``ActorPath.toSerializationFormatWithAddress`` differs from ``toString`` if the address does not already have ``host`` and ``port`` components, i.e. it only inserts address information for local addresses. ``toSerializationFormatWithAddress`` also adds the unique id of the actor, which will change when the actor is stopped and then created again with the same name. Sending messages to a reference pointing the old actor will not be delivered to the new actor. If you do not want this behavior, e.g. in case of long term storage of the reference, you can use ``toStringWithAddress``, which does not include the unique id. This requires that you know at least which type of address will be supported by the system which will deserialize the resulting actor reference; if you have no concrete address handy you can create a dummy one for the right protocol using ``new Address(protocol, "", "", 0)`` (assuming that the actual transport used is as lenient as Akka’s RemoteActorRefProvider). There is also a default remote address which is the one used by cluster support (and typical systems have just this one); you can get it like this: .. includecode:: code/docs/serialization/SerializationDocTest.java :include: external-address-default Deep serialization of Actors ---------------------------- The recommended approach to do deep serialization of internal actor state is to use Akka :ref:`persistence-java`. A Word About Java Serialization =============================== When using Java serialization without employing the :class:`JavaSerializer` for the task, you must make sure to supply a valid :class:`ExtendedActorSystem` in the dynamic variable ``JavaSerializer.currentSystem``. This is used when reading in the representation of an :class:`ActorRef` for turning the string representation into a real reference. :class:`DynamicVariable` is a thread-local variable, so be sure to have it set while deserializing anything which might contain actor references. External Akka Serializers ========================= `Akka-protostuff by Roman Levenstein <https://github.com/romix/akka-protostuff-serialization>`_ `Akka-quickser by Roman Levenstein <https://github.com/romix/akka-quickser-serialization>`_ `Akka-kryo by Roman Levenstein <https://github.com/romix/akka-kryo-serialization>`_ Other Akka source code examplesHere is a short list of links related to this Akka serialization.rst source code file: |
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