HibernateEnvers

Hibernate Envers is a module of the Hibernate ORM project that provides auditing and versioning for persistent entities. It automatically records historical states of entities by maintaining audit tables and revision information. By annotating an entity with @Audited, Envers tracks changes to that entity; fields can be excluded with @NotAudited. Relationships can also be audited with @AuditMappedBy.

Under the hood, Envers uses a revision entity (default DefaultRevisionEntity) that stores a revision number and timestamp. Each change to an audited entity is logged in a corresponding audit table, typically named Entity_AUD, with columns for all fields plus REV and REVTYPE to indicate insert, update, or delete. A separate revision table stores metadata about each revision.

Usage involves enabling Envers in the configuration by including the hibernate-envers module and enabling auditing via annotations. The API provides AuditReader and AuditQuery for retrieving historical data, such as the state of an entity at a given revision or all revisions within a range.

Customization allows you to supply your own revision entity with @RevisionEntity to store extra information. Auditing of relationships can be configured with @AuditMappedBy and related mapping attributes.

Limitations include performance overhead and schema complexity. Not all field types are auditable by default, and auditing large collections requires careful design.

Hibernate Envers is commonly used for regulatory compliance, data recovery, and historical data analysis, and integrates with JPA and Hibernate's event system to provide a transparent audit trail.