Issue with serializing Hibernate objects using XStream

Question

I\'ve been facing this issue where, the hibernate objects on serialization produces unexpect xmls containing all the instrumented code from Hibernate.

We did some cleani

Answer 1

I've not used XStream before, but I have serialized Hibernate-managed entities. It isn't fun.

There are two big issues:

• Lazy loading;
• One-to-many relationships.

The former is obvious - you need the actual data to serialize. The latter is less so - any one-to-many relationships you declare against collection interfaces (eg: Set) will get plugged by Hibernate's own (unserializable!) collection implementations. This may well be where Hibernate's classes are bleeding into your objects.

I ended up writing reflective code (actually introspective) that did this:

1. With the session open, touched the entire object graph to force-load any unloaded entities;
2. Closed the Hibernate session (including any transactions involving its connection);
3. Walked the object graph, replacing any lists, sets or maps with instances of ArrayList, HashSet or HashMap (known-serializable collections).

Note that step 2 is important - if you replace the collections prior to closing the session, Hibernate will just put its own collections right back upon close...

Edit: @cliff.meyers spotted a detail of the implementation I forgot to mention: if you do this, you need to limit object graph walking only to your own entities, and watch for circular reference paths (eg: by caching references to objects you've already walked).