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Java Data Objetcs


The Java community needs a standard way to store Java objects persistently in transactional data stores. Furthermore, it needs a standard way to treat relational database data as Java objects, and a standard way to define transactional semantics associated with those objects. 

The Java Data Objects (JDO) specification provides for interface-based definitions of data stores and transactions; and selection and transformation of persistent storage data into native Java programming language objects.



JDO is designed to work on all Java platforms. All Java platforms - desktop, server, personal, embedded, and card - can use this API to access data.

Existing specifications for persistence include JDBC, SQLJ, and java.util.Serializable. The JDBC and SQLJ mechanisms provide for query, transactions, and large capacity storage, but require that users learn another language (SQL). JDO allows users to specify their application program logic, including queries, entirely in Java, and express the mapping, if any, to the database with a separate mechanism. The java.util serialization protocol provides for persistence, but it does not offer query capability, transactional behavior, nor large capacity data storage. In addition, both the serialization and SQL APIs require that the programmer explicitly fetch and store Java objects from a database; JDO proposes Transparent Persistence, doing this automatically.

JDO is therefore, a high level API that may be implemented using lower level APIs like JDBC or SQLJ PART 0 to store data. This specification provides for interface-based definition of data stores, transactions, selection, and transformation of persistent storage data into native Java objects. 

There are several major parts of the specification:

  • the semantics of persistence with regard to transactions; 
  • the mapping (default and user-specified) of data types between data stores and Java objects;
  • the interactions of transactional objects with Enterprise Java Beans bean- and container-managed persistence; 
  • the selection of objects from the data store based on Java expressions.
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