DataNucleus（通过jpa和jdo接口访问多中数据源）

DataNucleus主页：http://www.datanucleus.org/index.html

简介：

DataNucleus项目为Java运行环境中的应用数据提供了管理，它提供了标准的接口（JDO, JPA）来访问各种类型的数据库资源，如RDBMS, ODBMS, Map-based, Web-based, 
documents, graph-based等等，并且你可以利用同样的API来操作所有你的数据，示图如下：

可见，对于HBase这样的NoSQL数据库也提供了JDO/JPA的接口。

最新版本3.2的信息如下：

January 1st 2013- DataNucleus Access Platform 3.2 ("Copernicus") Milestone 2 is released. DataNucleus Access Platform provides persistence and retrieval of Java objects to/from a wide range of datastores including relational, web-based, map-based, and documents. Version 3.2 Milestone 2 includes the following changes

• JDO : ability to mark all classes as detachable, overriding metadata
• JDO : add convenience accessor for "detachedState" of an object
• JDO : provide access to the native query performed by JDOQL
• JPA : add convenience accessor for "detachedState" of an object
• JPA : provide access to the native query performed by JPQL
• JPA : support surrogate version on a class
• JPA : fix to exception throwing when using JTA in a JavaEE environment
• JPA : support for JPA2.1 "Generate Schema" feature
• JPA : improved logix for finding a persistence-unit with a name, and flag duplicate units with the same name
• JPA : default to not add classTransformer in JavaEE environment (so user has to enable it)
• Update to JMX beans definitions for compliance
• Bundle (repackaged) ASM into datanucleus-core for cleaner usage
• Fix missing "PreMainClass" for enhancer so runtime enhancement works
• Moved "mapped datastores" code into RDBMS plugin (from datanucleus-core) since only used there
• Add pooling for ExecutionContext and ObjectProvider objects for performance.
• Fix to persist of N-1 relation with detached owner so we don't get multiple element objects
• Fix to ClassLoaderImpl/MetaDataUtils to preserve ordering whilst removing dups
• Provide access to native query being invoked by a JDOQL/JPQL query
• RDBMS : fix to use of named parameters in range clause of query
• RDBMS : add statement batching to shifting process for elements in a List
• RDBMS : fix to schema generation when we have "subclass-table" part way down an inheritance tree
• MongoDB : improvement for polymorphic queries to make use of discriminator column and handle all in single query
• MongoDB : improvement to deletion process to not reload same fields multiple times
• HBase : support for Bloom filters, in-memory and various other options (Nicolas Seyvet)
• Excel : make "poi-ooxml" dependency optional since not needed with XLS
• Various minor bug fixes and improvements

This release is downloadable under an Apache 2 license from the DataNucleus community site.