Keeping track of changed properties in JPA : <p>Currently, I'm working on a Java EE project with some non-trivial requirements regarding persistence management. Changes to entities by users first need to be applied to some working copy before being validated, after which they are applied to the "live data". Any changes on that live data also need to have some record of them, to allow auditing.</p>

<p>The entities are managed via JPA, and Hibernate will be used as provider. That is a given, so we don't shy away from Hibernate-specific stuff. For the first requirement, two persistence units are used. One maps the entities to the "live data" tables, the other to the "working copy" tables. For the second requirement, we're going to use Hibernate Envers, a good fit for our use-case.</p>

<p>So far so good. Now, when users view the data on the (web-based) front-end, it would be very useful to be able to indicate which fields were changed in the working copy compared to the live data. A different colour would suffice. For this, we need some way of knowing which properties were altered. My question is, what would be a good way to go about this?</p>

<p>Using the JavaBeans API, a <code>PropertyChangeListener</code> could suffice to be notified of any changes in an entity of the working copy and keep a set of them. But the set would also need to be persisted, since the application could be restarted and changes can be long-lived before they're validated and applied to the live data. And applying the changes on the live data to obtain the working copy every time it is needed isn't feasible (hence the two persistence units).
We could also compare the working copy to the live data and find fields that are different. Some introspection and reflection code would suffice, but again that seems rather processing-intensive, not to mention the live data would need to be fetched.
Maybe I'm missing something simple, or someone know of a wonderful JPA/Hibernate feature I can use. Even if I can't avoid making (a) separate database table(s) for storing such information until it is applied to the live data, some best-practices or real-life experience with this scenario could be very useful.</p>

<p>I realize it's a semi-open question but surely other people must have encountered a requirement like this. Any good suggestion is appreciated, and any pointer to a ready-made solution would be a good candidate as accepted answer.</p>
