Java Persistence API (JPA) - A Brief Overview

Java Persistence API (JPA) A Brief Overview By Scott Rabon

We have come a long way • Java application persistence history – JDBC – EJB Entity Beans 1

Industry answered the call • Proprietary persistence products were introduced – JBoss Hibernate – Oracle Top Link 2

Why Another Standard • Standard goes deeper than a product • Can be implemented by different vendors • Developers code to interface, not implementation 3

A Standard Is Born JSR 220 – EJB 3.0 Specification Java Persistence API part of EJB 3.0 Specification 4

JPA Fun Facts • JSR 220 formed May 2003 • Released May 2006 • Expert group consisted of industry ORM developers 5

JPA – Designed for Ease of Use • Main goal of design team • Elegant, powerful and flexible • Easy to learn 6

Aspects: POJO Persistence • Objects are POJO’s • Mapping is metadata driven • External XML or annotation based 7

Aspects: Non Intrusiveness • API does not intrude on objects • API exists as a separate layer from persistent objects • Objects are “unaware” of the API 8

Aspects: Object Queries • Query across entities and relationships • Expressed in Java Persistence Query Language (JPQL) • Uses a schema abstraction 9

Aspects: Mobile Entities • Detachment Model • Move entities between JVM’s • Can change state anywhere along the way • Reattach upon return 10

Aspects: Simple Configuration • Java SE 5 Annotations • XML • Heavy use of defaults 11

Aspects: Integration and Testability • Challenge: Testing on an app server • API works outside application server – Two tier apps – Unit tests and automated testing frameworks 12

Entities Not same as entity beans 13

Entity Characteristics - Persistability • Entities must be persistable • State can be represented in a data store • Entities can be manipulated without having persistent repercussions – app must use API 14

Entity Characteristics - Identity • Key that uniquely identifies an instance • Persistent identity • Equivalent to primary key 15

Entity Characteristics - Transactionality • Adds, updates and deletes normally occur in a transaction • Changes succeed or fail atomically • In memory entities 16

Entity Characteristics - Granularity • Not primitives, wrappers, built-in objects • Are business domain objects that mean something • Should be fairly lightweight objects 17

Entity Manager • Interface encapsulating most persistence functionality • Set of managed instances is named persistence context 18

Queries • Use JPQL syntax • Can be defined statically (named) or dynamically • Dynamic queries supply query criteria 19

JPA’s future - Independence • Break free from the EJB specification • Will get it’s own JSR for future evolution 20

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Java Persistence API (JPA) - A Brief Overview

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