Java Persistence API

The Java Persistence API (JPA) is a Java application programming interface specification that describes the management of relational data in applications using Java Platform, Standard Edition and Java Platform, Enterprise Edition.

Persistence in this context covers three areas:

The reference implementation for JPA is EclipseLink.

The final release date of the JPA 1.0 specification was 11 May 2006 as part of Java Community Process JSR 220. The JPA 2.0 specification was released 10 December 2009. The JPA 2.1 specification was released 22 April 2013.

A persistence entity is a lightweight Java class whose state is typically persisted to a table in a relational database. Instances of such an entity correspond to individual rows in the table. Entities typically have relationships with other entities, and these relationships are expressed through object/relational metadata. Object/relational metadata can be specified directly in the entity class file by using annotations, or in a separate XML descriptor file distributed with the application.

The Java Persistence Query Language (JPQL) makes queries against entities stored in a relational database. Queries resemble SQL queries in syntax, but operate against entity objects rather than directly with database tables.

Prior to the introduction of EJB 3.0 specification, many enterprise Java developers used lightweight persistent objects, provided by either persistence frameworks (for example Hibernate) or data access objects instead of entity beans. This is because entity beans, in previous EJB specifications, called for too much complicated code and heavy resource footprint, and they could be used only in Java EE application servers because of interconnections and dependencies in the source code between beans and DAO objects or persistence framework. Thus, many of the features originally presented in third-party persistence frameworks were incorporated into the Java Persistence API, and, as of 2006, projects like Hibernate (version 3.2) and TopLink Essentials have become themselves implementations of the Java Persistence API specification.

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