A Serializer represents a bimap between an object and an array of bytes representing that object.

For serialization of data that need to evolve over time the SerializerWithStringManifest is recommended instead of Serializer because the manifest (type hint) is a String instead of a Class. That means that the class can be moved/removed and the serializer can still deserialize old data by matching on the String. This is especially useful for Akka Persistence.

The manifest string can also encode a version number that can be used in fromBinary to deserialize in different ways to migrate old data to new domain objects.

If the data was originally serialized with Serializer and in a later version of the system you change to SerializerWithStringManifest the manifest string will be the full class name if you used includeManifest=true, otherwise it will be the empty string.

Serializers are loaded using reflection during akka.actor.ActorSystem start-up, where constructors are tried in order:

• taking exactly one argument of type akka.actor.ExtendedActorSystem; this should be the preferred one because all reflective loading of classes during deserialization should use ExtendedActorSystem.dynamicAccess (see akka.actor.DynamicAccess)
• taking exactly one argument of type akka.actor.ActorSystem
• taking exactly one argument of type akka.actor.ClassicActorSystemProvider
• without arguments
• taking two arguments of type akka.actor.ExtendedActorSystem and String where the second String argument is the binding name
• taking two arguments of type akka.actor.ActorSystem and String where the second String argument is the binding name
• taking two arguments of type akka.actor.ClassicActorSystemProvider and String where the second String argument is the binding name

Be sure to always use the akka.actor.DynamicAccess for loading classes! This is necessary to avoid strange match errors and inequalities which arise from different class loaders loading the same class.