Java Dated Object

The Java Dated Objects (or JDO ) is a data-processing standard based on Java.

Standard Java giving access to the data in a transparent and unified way. The standard is managed within the framework of JSR of SUN.

The ease of use of JDO based on the handling of POJOs (Lime pit Old Objects Java) made the success of this standard. The developer can handle the objects without worrying about the Persistance.

Potentially, the standard gives access to data sources of various nature.

Three main categories of implementations exist:

  • the implementations which support only DBMS relational

  • the implementations which support only DBMS Object
  • the implementations which support heterogeneous data sources (SGBDR, SGBDO, XML, Mainframe) and also the access to services (WebServices, JMS (Java messaging service), JCA (Java Connector Architecture), Cobol). In the supporting cases of the implementations of the heterogeneous sources, one of the benefit brought is the flexibility of the Information system. It becomes indeed possible to change data source by simple parameter setting.

History of JDO

JDO is the first specification of Java allowing transparent persistence (JSR12).

JDO was revolutionist in the direction or for the first time the developers could concentrate on the models objects and not on the technical code of access to the DBMS.

JDO 1.0 was accepted like the Java standard of management of persistence in April 2002.

JDO 2.0 began in August 2003. At the end of 2005, JDO 2.0 is quasi finalized under Apache Software Foundation. In March 2005 the final vote on JDO 2.0 is approved unanimously by SUN, BEA, Oracle, Borland, HP, Intel, Fujitsu, SAP, Google, IBM… On 16 voters only JBoss (Hibernate) did not vote.

Innovations of JDO 2.0

  • Attachment and Détachement

  • Interface javax.jdo.FetchPlan and " fetch groups" named
  • JDOQL projections and aggregats (count, sum, min, max, etc)
  • JDOQL named requests
  • JDOQL suppression by request
  • native Support of the requests SQL for the relational data sources
  • Interface javax.jdo.DataStoreCache to control the mask of second level
  • Interface javax.jdo.JDOConnection to recover an direct access with subjacent connection

External references

Implementations of JDO

  • XIC (Platform of Intermediation of Xcalia).

  • JPox
  • ObJectRelationalBridge (OJB)
  • the East ODBMS
  • Speedo an implementation open-source of the consortium ObjectWeb.

Additional details

  • JDO on the site of SUN
  • JSR 243: JDO 2
  • JSR 12: JDO 1
  • Specification Java on Historical persistence
  • of JDO
  • Laboratory of Sun technologies: course on JDO

See also

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