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Introduction to JPA

This introduction to the Java Persistence API (JPA) covers its purpose in addressing the challenges of Object-Relational Mapping (ORM) and the impedance mismatch between object-oriented programming languages and relational databases. It explains how JPA integrates with Java EE 5, detailing the role of EntityManager and JPQL (Java Persistence Query Language). Additionally, the document discusses various persistence providers such as Hibernate and Oracle's TopLink, and provides insights into how JPA standardizes O/R mapping, making data persistence in Java applications more efficient.

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Introduction to JPA

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  1. Introduction to JPA Java Persistence API Introduction to JPA

  2. ORMObject-Relational Mapping • Problem • Object oriented programming languages • Relational DBMS • Several ORM frameworks has tried to ”fix” the problem • Example: Hibernate • JPA standardizes O/R mapping Introduction to JPA

  3. Impedance mismatchEJB 3 In Action, page 252 Introduction to JPA

  4. Java EE 5 • JPA is part of Java EE 5 • JPA works between the Business Tier and the EIS tier (Enterprise Information System) • Figure from ”Java EE 5 Tutorial” • http://java.sun.com/javaee/5/docs/tutorial/doc/bnaay.html Introduction to JPA

  5. Java EE 5 • Some Java EE 5 containers • GlassFish from Sun • Application Server from Oracle • JBoss • WebSphere from IBM • WebLogic from BEA • BEA was recently acquired by Oracle • Apache Tomcat • Not a full Java EE container, only a web container Introduction to JPA

  6. Java Persistence API • JPA is an API • Implemented by a persistence provider • Like JDBC is an API implemented by • Some persistence providers • Hibernate from JBoss • TopLink from Oracle • Kodo from BEA • recently acquired by Oracle Introduction to JPA

  7. The class EntityManager • EntityManager is the most important class of JPA • Full name javax.persistence.EntityManager • Some methods of EntityManager • T find(primaryKey) • Query createQuery(String jpql) • Creates a JPQL query • Query createNativeQuery(String sql) • Creates a SQL query • Some methods of Query • List getResultList() • Executes a Query and returns a list of objects Introduction to JPA

  8. Java Persistence Query Language (JPQL) • Very much like ordinary SQL • But not specific to any DBMS • JPA converts JPQL to ordinary SQL for the actual DBMS Introduction to JPA

  9. EJB 3 • EJB 3 • Enterprise Java Beans • Important part of Java EE 5 • Much simpler than EJB 2 • POJO + annotations • Plain Old Java Objects • EJB classes can • Create database tables or • Be created from database tables Introduction to JPA

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