One of the key aspects of Infinispan is that it often needs to marshall or
unmarshall objects in order to provide some of its functionality. For
example, if it needs to store objects in a write-through or write-behind
cache store, the objects stored need marshalling. If a cluster of
Infinispan nodes is formed, objects shipped around need marshalling. Even
if you enable storing as binary, objects need to marshalled so that they
can be lazily unmarshalled with the correct classloader.
Using standard JDK serialization is slow and produces payloads that are too
big and can affect bandwidth usage. On top of that, JDK serialization does
not work well with objects that are supposed to be immutable. In order to
avoid these issues, Infinispan uses JBoss Marshalling for
marshalling/unmarshalling objects. JBoss Marshalling is fast, provides
very space efficient payloads, and on top of that, allows users to
construct objects themselves during unmarshalling, hence allowing objects
to carry on being immutable.
Starting with 5.0, users of Infinispan can now benefit from this marshalling
framework as well. In the simplest possible form, users just need to
implementation for the type that they want
to marshall/unmarshall, and then annotate the marshalled type class with
indicating the externalizer class to use and that's
all about it. At runtime JBoss Marshaller will inspect the object and
discover that's marshallable thanks to the annotation and so marshall it
using the externalizer class passed.
It's common practice to include externalizer implementations within the
classes that they marshall/unmarshall as
public static classes
To make externalizer implementations easier to code and more typesafe, make
sure you define type <T> as the type of object that's being
Even though this way of defining externalizers is very user friendly, it has
- Due to several constraints of the model, such as support different
versions of the same class or the need to marshall the Externalizer
class, the payload sizes generated via this method are not the most
- This model requires for the marshalled class to be annoated with
but a user might need to provide an Externalizer
for a class for which source code is not available, or for any other
constraints, it cannot be modified.
- The use of annotations by this model might be limiting for framework
developers or service providers that try to abstract lower level
details, such as the marshalling layer, away from the user.
If you're affected by any of these disadvantages, an alternative mechanism
to provide externalizers is available via
More details can be found in this interface's javadoc.
Please note that even though Externalizer is marked as
the need to marshall the externalizer is only really needed when developing
user friendly externalizers (using
instances do not require the externalizer to be serializable since the
externalizer itself is not marshalled.
Even though it's not strictly necessary, to avoid breaking compatibility
with old clients,
this requirement is only needed for those user friendly externalizers.
There's a chance that in future major releases
any more, hence we strongly recommend that any
user-friendly externalizer users mark their externalizer implementations as
- Galder Zamarreño