The Envers project makes it simple to version entities. The only thing required is annotating them with @Versioned. Storing historical data (versions) is completely transparent to the developer. He/she may interact with the entities as always.
Not only basic properties of an entity can be versioned, but also relations, making it possible to view parts of the database as they were at a given revision (each revision has an associated timestamp, one revision = one transaction, in which versioned data has changed).
Moreover, Envers provides a straightforward interface for retrieving historical data, a criteria-like query interface, and the possibility to store additional information alongside each revision.
Envers works with Hibernate and Hibernate Entity Manager.
