[Jdbm-developer] more thoughts on jdbm serialization.

[Thompson, B. B. <BRY...@sa...>]

I've been quiet while finishing up some test cases and thinking some
more about how to approach serialization of "compound" records.  The
drawbacks with using the Externalizable interface are: (1) it does not
take advantage of transparent versioning of serializers -- you have
to handle your own versioning of your externalizable format; and (2)
it does not separate the serialization logic from the business object.

I've been looking at how easy it would be to support a stream oriented
serializer interface (StreamSerializer) with some methods similar to
those on the Externalizable interface, but unlike the Externalizable
interface (and like the Serializer interface) it is designed to be
implemented by specific serialization classes, so it would decouple
the business objects and their serialization and also provide for
transparent versioning of serializers.  A non-goal of StreamSerializer
would be BLOB support.  I think that streaming very large objects to
the store deserves a separate API.  The StreamSerializer would target
complex records, such as BPage, but not very large records.  The result
of applying a StreamSerializer would be a byte[] and that byte[] would
be handled in the normal manner by the recman.

There are two flys in the ointment.  First we would need to have a
common interface for Serializer and StreamSerializer, though perhaps
the StreamSerializer would only be used with the extensible serialization
support, otherwise the new interface would wind up in the insert, update,
and fetch methods on the recman, which would change the method signatures
(code compatibility).

The other issue is that this basically means implementing ObjectOutput
and ObjectInput ourselves - either over DataOutputStream and
DataInputStream or using the mechanisms available to subclass
ObjectOutputStream and ObjectInputStream.  I've looked into the subclass
option a bit and it does not offer much (really anything) over just
reimplementing ObjectOutput and ObjectInput ourselves.  All of the
really important methods are private or final and when there is a means
to extend the class, e.g., writeObjectOverride, then the methods and
classes that you would want to use are private.

Thoughts?

-bryan