An Externalizer is a class that knows how to marshall a given object type to a byte array, and how to unmarshall the contents of a byte array into an instance of the object type. Externalizers are effectively an Infinispan extension that allows users to specify how their types are serialized. The underlying Infinispan marshalling infrastructure builds on JBoss Marshalling, and offers efficient payloads and stream caching. This provides much better performance than standard Java serialization.