Java Data Objects
The Java Data Objects ( JDO ) are an official Sun specification for a vendor-neutral framework for persistent storage of Java objects.
In the JDO specification a uniform interface for accessing persistent data is defined. The way the physical storage is not fixed. Thus, the object information in databases (relational or object-oriented), files, or further memories are stored.
Using JDO, the programmer can manipulate data objects without knowledge of the memory mechanisms. Thus developers no longer need to deal with the internals of databases, they can focus on the pure application logic.
Development
JDO was influenced by the Object Database Management Group ( ODMG ) and launched as a JSR -12 in 1999. The first version of JDO was adopted in May 2001 by well-known companies such as Sun, IBM and Apple. For JDO 1.0 was developed by Sun both the API (specification), and Technology Compatibility Kit ( TCK compatibility tests) and Reference Implementation (RI, reference implementation ) developed and deployed. JDO 1 was later completely handed over to the Apache Software Foundation, which serves as part of the Apache DB Project.
Since version 2 from 1 May 2006, JDO, as is evident from JSR -243, advanced by Apache. When choosing the reference implementation for JDO 2, the Apache OJB own project was due to time constraints ignored and instead JPOX (now succeeded by DataNucleus ) as the RI.
The JDO 2.1 maintenance release of 2 August 2007 saw support for Java 5 annotations, generics and enumerated types ( enum). The JDO 2.2 release of 10 October 2008 was merely a bug fix release.
EJB 3.0, respectively, the Java Persistence API (JPA ) was significantly influenced by lightweight approaches like JDO or Hibernate also.
Assessment
Sun's step to make JDO is understandable and consistent, since it can be problematic to advance two different Persistenzansätze parallel and equal. Although there exist many JDO implementations and support ( free and commercial ), also is just JDO 2 very powerful, nevertheless shows that the other standardized solutions are strengthened by a strategic shift away Sun. So EJB 3 provides as an implementation of the Java Persistence API is now comparable opportunities as other lightweight solutions. So shows a comparison of JDO and EJB 3, that both solutions can also work with the Standard Edition. A comparison of JDO and Hibernate shows that here also get along both solutions with POJOs.