OpenJPA

OpenJPA is an open-source Java persistence framework that implements the Java Persistence API (JPA). It provides object-relational mapping (ORM) between Java objects and relational database tables, enabling applications to persist, query, and manage data using standard JPA concepts such as entities, relationships, and transactions.

A key feature of OpenJPA is its support for JPQL and the Criteria API, allowing developers to write portable queries that operate on entity models rather than database tables. It includes tooling for metadata handling, schema generation, and integration with various transaction managers. OpenJPA is designed to run in Java SE or Java EE environments and can be used with different application servers and frameworks.

OpenJPA employs bytecode enhancement to support efficient lazy loading and dirty checking of entities. This enhancement can be performed at build time or runtime, helping improve performance and reduce the need for invasive proxies. The provider is designed to be pluggable and database-agnostic, working with JDBC drivers for multiple relational databases and various caching and transaction configurations.

As an Apache Software Foundation project, OpenJPA is distributed under the Apache License 2.0. It aims to offer a standards-based, enterprise-grade JPA implementation that can serve as an alternative to other providers. OpenJPA can be used for both standalone Java applications and enterprise applications that require portable object-relational mapping and robust data management.

See also Java Persistence API, Hibernate, EclipseLink, and Apache.