AuditReader

AuditReader is a component of Hibernate Envers that provides read-only access to the historical state of persisted entities. It enables applications to reconstruct past entity states and analyze how data has changed over time by querying audit data that Envers maintains for audited entities.

To use AuditReader, you obtain it from the current JPA or Hibernate session via AuditReaderFactory.get(entityManager). Audit data is stored in separate audit tables (commonly named with an _AUD suffix) and is tied to revisions recorded in the REVINFO table. AuditReader itself does not write data; it only reads and interprets existing audit records.

Key capabilities include retrieving an entity as it existed at a specific revision, listing all revisions for a given entity, and obtaining the timestamp of a particular revision. Common methods are find(entityClass, id, revision), getRevisions(entityClass, id), and getRevisionDate(revision). AuditReader also supports building advanced queries through createQuery(), which can target entities at a given revision, entities changed in a revision, or entities at a particular property state. Queries can also expose the RevisionType to indicate added, modified, or deleted changes.

Configuration and usage considerations: Envers requires enabling auditing and annotating relevant entities with @Audited. Audit tables and revision information are created automatically unless customized. While AuditReader provides powerful read access to historical data, auditing introduces additional storage requirements and potential performance considerations for write operations, and complexity can increase when auditing associations and complex relationships.