Java Persistence API

The Java Persistence API, sometimes referred to as JPA, is a Java programming language framework managing relational data in applications using Java Platform, Standard Edition and Java Platform, Enterprise Edition.

The Java Persistence API originated as part of the work of the JSR 220 Expert Group. JPA 2.0 is the work of the JSR 317 Expert Group.

Persistence in this context covers three areas:

Contents

History

The final release date of the JPA 1.0 specification was 11 May 2006 as part of JSR 220. The JPA 2.0 specification was released 10 Dec, 2009.

Entities

A persistence entity is a lightweight Java class whose state is typically persisted to a table in a relational database. Instances of such an entity correspond to individual rows in the table. Entities typically have relationships with other entities, and these relationships are expressed through object/relational metadata. Object/relational metadata can be specified directly in the entity class file by using annotations, or in a separate XML descriptor file distributed with the application.

The Java Persistence Query Language

Further information: Detailed information is available at Wikibook's Java Persistence/Querying article

The Java Persistence Query Language (JPQL) makes queries against entities stored in a relational database. Queries resemble SQL queries in syntax, but operate against entity objects rather than directly with database tables.

Motivation for creating the Java Persistence API

Many enterprise Java developers use lightweight persistent objects provided by open-source frameworks or data access objects instead of entity beans: entity beans and enterprise beans had a reputation of being too heavyweight and complicated[clarify], and one could only use them in Java EE application servers. Many of the features of the third-party persistence frameworks were incorporated into the Java Persistence API, and, as of 2006, projects like Hibernate (version 3.2) and TopLink Essentials have become implementations of the Java Persistence API.

Related Technologies

Enterprise JavaBeans

The EJB 3.0 specification (itself part of the Java EE 5 platform) included a definition of the Java Persistence API. However, end-users do not need an EJB container or a Java EE application server in order to run applications that use this persistence API.[1] Future versions of the Java Persistence API will be defined in a separate JSR and specification rather than in the EJB JSR/specification.

The Java Persistence API replaces the persistence solution of EJB 2.0 CMP (Container Managed Persistence).

Java Data Objects API

Main article: Java Data Objects

The Java Persistence API was developed in part to unify the Java Data Objects API, and the EJB 2.0 Container Managed Persistence (CMP) API. As of 2009 most products supporting each of those APIs support the Java Persistence API.

The Java Persistence API specifies persistence only for relational database management systems. That is, JPA focuses on object-relational mapping (ORM) (note that there are JPA providers who support other database models besides relational database, but this is outside the scope of what JPA was designed for). Refer to JPA 2 spec section 1 introduction for clarification of the role of JPA, which states very clearly "The technical objective of this work is to provide an object/relational mapping facility for the Java application developer using a Java domain model to manage a relational database."


The Java Data Objects specification supports ORM, as well as persistence to other types of database models, for example flat file databases.

Service Data Object API

Main article: Service Data Objects

The designers[2] of the Java Persistence API aimed to provide for relational persistence, with many of the key areas taken from object-relational mapping tools such as Hibernate and TopLink. Java Persistence API improved on and replaced EJB 2.0, evidenced by its inclusion in EJB 3.0. The Service Data Objects (SDO) API (JSR 235) has a very different objective to the Java Persistence API and is considered [3][4] complementary. The SDO API is designed for service-oriented architectures, multiple data formats rather than only relational data, and multiple programming languages. The Java Community Process manages the Java version of the SDO API; the C++ version of the SDO API is managed via OASIS.

Hibernate

Main article: Hibernate (Java)

Hibernate provides an open source object-relational mapping framework for Java. Versions 3.2 and later provide an implementation for the Java Persistence API.[5]

Gavin King founded[6] Hibernate. He represented JBoss on JSR 220,[7] the JCP expert group charged with developing JPA. This led to ongoing controversy and speculation surrounding the relationship between JPA and Hibernate. Sun Microsystems has stated[8] that ideas came from several frameworks, including Hibernate and JDO.

JPA 2.0

Development of a new version of JPA, namely JPA 2.0 JSR 317 was started in July 2007. JPA 2.0 was approved as final on December 10, 2009.

The focus of JPA 2.0 was to address features that were present in some of the popular ORM vendors but couldn't gain consensus approval for JPA 1.0.

The main features included in this update are:

  • Expanded object-relational mapping functionality
    • support for collections of embedded objects[clarify]
    • multiple levels of embedded objects
    • ordered lists
    • combinations of access types
  • A criteria query API
  • standardization of query 'hints'[clarify]
  • standardization of additional metadata to support DDL generation
  • support for validation

Vendors supporting JPA 2.0

See also

References

  1. ^ Hibernate EntityManager: Java SE environments
    Hibernate EntityManager: Obtaining an EntityManager in a Java SE environment
  2. ^ "JSR 220 Members". http://jcp.org/en/jsr/detail?id=220.
  3. ^ Barreto, Charlton. "SDO and JPA". Digital Walkabout. http://charltonb.typepad.com/weblog/2007/10/sdo-and-jpa.html. Retrieved 5 May 2011.
  4. ^ Edwards, Mike. "SDO and Java Persistence Architecture (JPA)". Open SOA. osoa.org. http://www.osoa.org/display/Main/SDO+and+Java+Persistence+Architecture+%28JPA%29. Retrieved 5 May 2011.
  5. ^ "hibernate.org - Java Persistence with Hibernate". JBoss. http://www.hibernate.org/397.html. Retrieved 2008-11-17. "Hibernate implements the Java Persistence object/relational javaAPI and persistence management interfaces"
  6. ^ "Manning: Java Persistence with Hibernate". Manning. "Gavin King -- the founder of the Hibernate project"
  7. ^ "JBoss.com - Industry Leadership". JBoss. http://www.jboss.com/company/leadership. Retrieved 2008-11-17. "JSR 220, EJB 3.0 Spec Committee, Gavin King, Bill Burke, Marc Fleury"
  8. ^ "Java Persistence API FAQ". Sun Microsystems. Archived from the original on 2008-08-22. http://web.archive.org/web/20080822023926/http://java.sun.com/javaee/overview/faq/persistence.jsp. Retrieved 2010-07-01. "The Java Persistence API draws upon the best ideas from persistence technologies such as Hibernate, TopLink, and JDO"

External links

General info

Documentation

Tutorials

Java Persistence API
fonte: https://web.archive.org/web/20130131234129/http://en.wikipedia.org/wiki/Java_Persistence_API