I've used the serializable-type to get hibernate to store third-party objects I use as delegates in my own objects. The object is accessible as a property in my object.

This seemed like the best choice since the alternatives (as far as I know) was:

1. To create a hibernate-mapping of the third party object (of which I know little other than that it is serializable).

2. To include all parameters needed in my object to re-instantiate the 3rd party object when needed, which in my case can be arbitrarily complex.

The serializable-type however just plain works, with little effort on my part. There is however a catch:

In my ejbs, the objects are requested each session. Hibernates caching speeds everything up nicely, EXCEPT for the serialized objects. Profiling reveals that only the bytes are cached, and the object is de-serialized each time I ask for it. Is there a way to get hibernate to cache the deserialized object, or do I have to implement my own cache?

You should be able to use a CompositeUserType to implement a customized cache assembly/disassembly algorithm. However, I don't think this would be right - objects have to be deep copied in and out of the cache.

A colleague of mine implemented a quick-and-ditry solution, by persisting the bytestream instead, and de-serializing on demand. This worked very well for our application, since the delegates are rarely used.