Primer for OpenJPA

最新推荐文章于 2025-11-26 15:59:01 发布

最新推荐文章于 2025-11-26 15:59:01 发布 · 87 阅读

文章标签：

本文详细介绍了OpenJPA作为Java持久化API的开源实现，如何与Weblogic、WebSphere和Geronimo应用服务器集成，以及它如何通过提供无数据库特定的Java API来存储和检索信息到后端数据库。文章还阐述了OpenJPA中的关键组件、实体类的设计、继承规则以及回调方法的概念。

OpenJPA is the open source implementation of Java Persistence API. It has been integrated with the Weblogic, WebSphere, and Geronimo application servers. JPA provides an agnostic Java-based API for storing and retrieving information to a backend database. It has a canonical query language named Java Persistence Query Language, or JPQL, that blends with the programming methods of Java and eliminates the need to tailor database queries for a particular database. However, JPA also supports native SQL which can be used for quick ports with a known backend database.

You'll need three artifacts to implement a JPA-compliant program:

An entity class
A persistence.xml file
A class through which you will insert, update, or find an entity

Since JPA is all about entity-relationship mapping, need to take a look at the design of the entity object. The entity object is nothing but a POJO class marked as an entity with the @Entity annotation.

JPA allows persistent classes to inherit from non-persistent classes, persistent classes to inherit from other persistent classes, and non-persistent classes to inherit from persistent classes.
The entity class should have a default no-argument constructor.
The entity class should not be final.
Persistent classes cannot inherit from certain natively-implemented system classes such asjava.net.Socketandjava.lang.Thread.
If a persistent class inherits from a non-persistent class, the fields of the non-persistent super class cannot be persisted.

JPA provides callback methods for performing actions at different stages of persistence operations. JPA provides listeners for these kinds of activities before and after each fetch, insert, or update operation. The callback methods can be annotated as any of the following: