java data jdo

最新推荐文章于 2025-12-02 21:20:38 发布

最新推荐文章于 2025-12-02 21:20:38 发布 · 100 阅读

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#java #数据库

本文详细介绍了Java Data Objects (JDO) 和 Java Persistence API (JPA) 的区别，并探讨了使用XML元数据和Java 5注解进行持久化的配置方法。文中还列举了指定元数据文件的具体位置。

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Persistence MetaData

JDO 1.0 and JDO 2.0 support specification of persistence using XML MetaData. JDO 2.1 adds on the ability to specify persistence using Java5 annotations.

XML MetaData

JDO (1.0.1, 2.0, 2.1) expects any XML MetaData to be specified in a file or files in particular positions in the file system. For example, if you have a class com.mycompany.sample.MyExample, JDO will look for any of the following files until it finds one (in the order stated) :-

META-INF/package.jdo
WEB-INF/package.jdo
package.jdo
com/package.jdo
com/mycompany/package.jdo
com/mycompany/sample/package.jdo
com/mycompany/sample/MyExample.jdo

In addition to specifying XML MetaData in a jdo file, if defining O/R mapping information you can also split this out into an ORM file. The locations for ORM files are similar in nature to those for JDO files.

META-INF/package-{mapping}.orm
WEB-INF/package-{mapping}.orm
package-{mapping}.orm
com/package-{mapping}.orm
com/mycompany/package-{mapping}.orm
com/mycompany/sample/package-{mapping}.orm
com/mycompany/sample/MyExample-{mapping}.orm

where {mapping} is a property specified by the user and may be "mysql" for ORM information for MySQL datastores, and "oracle" for ORM information for Oracle datastores, and so on.

Annotations

JDO 2.1 provides support for annotations. Classes and fields/properties can be annotated defining the persistence and, optionally, any ORM information.