OSGi Persistence With EclipseLink

OSGi Persistence Shaun Smith

OSGi Persistence
A core need for any enterprise Java application is persistence, e.g.:
Data maintained in a relational database
XML data maintained in files or exchanged with other systems
Persistence frameworks and standards designed for Java SE and EE are not typically OSGi compatible
EclipseLink provides a set of high performance and scalable Java persistence services for OSGi

Java Persistence: The Problem Space Customer id: int name: String creditRating: int CUST ID NAME C_RATING <customer id=“…”> <name>…</name> … </contact-info> </customer> Relational XML Java

Java Persistence Standards
Object-Relational: Java Persistence API (JPA)
JPA 1.0 part of EJB 3.0 standard (JSR 220)
JPA 2.0 independent standard (JSR 317)
Object-XML: Java Architecture for XML Binding (JAXB)
JAXB 2.x standardized in JSR 222
Object-XML: Service Data Objects
SDO 2.1.1 standardized in JSR 235

EclipseLink Architecture DBWS SDO EIS MOXy JPA XML Data Legacy Systems Databases Java SE Java EE OSGi Spring

EclipseLink Background
EclipseLink
Official name "Eclipse Persistence Services Project"
Founding Eclipse Runtime Project member
Lead by Oracle
Founded upon contribution of full TopLink source
Code base with 12 years of commercial usage
First comprehensive open source persistence solution

EclipseLink Distributions
Eclipse
Oracle
TopLink 11g
WebLogic Server
Sun GlassFish v3 (SunAS)
Replaces TopLink Essentials (JPA 2.0 Reference Implementation)
Spring Source
Spring Framework
Spring OSGi Bundle Repository
JOnAS Application Server 5.1

EclipseLink JPA
JPA 1.0 compliant implementation
Delivering the JPA 2.0 Reference Implementation
Java EE, Java SE, Web, Spring, and OSGi
Any JDBC/SQL compliant database
Extensible and pluggable
Schema generation
Key infrastructure:
Caching, Locking, Query Framework, Mapping, …
… plus many valuable advanced features

EclipseLink MOXy
Provides complete Object-XML mapping
Allows developers to work with XML as objects
Efficiently produce and consume XML
Supports Object-XML binding standard - JAXB
Provides external mapping file for complete control on how objects are mapped
domain model XML Data

EclipseLink SDO
SDO 2.1 provides the ability to:
Generate Java SDO classes (static SDOs) from an XML Schema.
Generate SDO Types and Properties at runtime from an XML Schema to create dynamic SDOs.
Generate an XML schema that corresponds to the types and properties of an SDO model.
This allows XML payloads in, for example, web services to include the schema that they conform to making the payload contents fully self describing.
Capture and marshal to XML the set of changes made to an SDO object graph in an SDO Change Summary.

EclipseLink OSGi Packaging
EclipseLink is available as a set of OSGi bundles:
JPA
org.eclipse.persistence.jpa—JPA implementation
org.eclipse.persistence.antlr—JPQL parsing
org.eclipse.persistence.asm—Byte code weaving
MOXy JAXB
org.eclipse.persistence.moxy—OXM/JAXB implementation
SDO
org.eclipse.persistence.sdo—SDO implementation
Core (used by all persistence services)
org.eclipse.persistence.core—shared infrastructure

OSGi Persistence Goal
Support usage of standard APIs
javax.persistence.Persistence.createEntityManagerFactory(..)
javax.xml.bind.JAXBContext.newInstance(..)
commonj.sdo.HelperProvider
Support modular packaging
E.g., domain model bundle(s), meta-data bundle, provider bundles
Decouple application from provider
Use JPA resolution to find suitable provider
Use JPA standard <provider> tag in persistence.xml to identify specific provider—no provider specific require-bundle or import-package

OSGi Persistence Challenges
JPA
javax.persistence.Persistence SPI scans classpath for providers
Provider needs access to domain model classes and application resources
Needs access to JDBC driver (addressed by RFC 122)
JAXB
Spec SPI does not support registration of providers
Provider needs access to domain model classes and application resources
Spec supports passing domain model classloader
SDO
Spec hardwires provider class and package—doesn't support multiple providers.

JPA—Bootstrap Problem
Persistence finds providers by loading all javax.persistence.spi .PersistenceProvider .xml files on classpath—but in OSGi it can’t see any.
javax.persistence Eclipselink JPA PersistenceProvider.xml Persistence requires

JPA—Service Based Solution
OSGi aware javax.persistence bundle that allows providers to register a persistence provider service.
When a provider bundle is started it registers with javax.peristence
When javax.persistence .Persistence is asked for a persistence unit it can ask registered providers to supply it.
javax .persistence PersistenceProvider register Providers Eclipselink JPA

JPA—Resource Access Problem
EclipseLink’s Persistence Provider can’t see persistence.xml, orm.xml , or Entities in PU bundle.
Eclipselink JPA persistence unit bundle persistence.xml orm.xml,…

JPA—Extender Pattern Solution
EclipseLink JPA uses extender pattern to identify persistence unit bundles.
EclipseLink keeps track of what persistence units are associated with what bundles (and what classloaders)
persistence unit bundle persistence.xml orm.xml,… bundle event OSGi Eclipselink JPA

EclipseLink Weaving Support
Uses (ASM) to introduce additional functionality into the ‘POJO’ domain classes
Used for
M:1 and 1:1 lazy fetching
Fetch Groups
Change Tracking
State Caching
Use is Optional (used by default when possible)
Static weaving also supported
Weaving of .class files before deployment
Dynamic weaving supported in Equinox through Adaptor Hook framework

More Problems and Solutions
JAXB OSGi
Support usage of standard APIs
javax.xml.bind.JAXBContext.newInstance(..)
Support modular packaging
E.g., domain model bundle(s), meta-data bundle, provider
No dependency on specific provider
JAXB SPI, unlike JPA, does not have a provider resolution mechanism that is OSGi friendly
Application must explicitly depend on specific provider
SDO OSGi
Support usage of standard commonj.sdo.HelperProvider
Application must use provider specific HelperProvider

Future Plans and Goals
Investigate further bundle splitting
As required by usage scenarios
Participate on development of OSGi RFC 143 JPA Integration
Weaving
Container vs. non-container API
JPA packaging configurations
Participate on JAXB and SDO expert groups to better support OSGi
Usability
Documentation and Examples

Summary
OSGi presents challenges when trying to use many frameworks built for Java SE/EE environments.
Before you commit to a framework you must evaluate whether it is OSGi friendly.
EclipseLink is the only comprehensive persistence framework shipping with support for OSGi!

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OSGi Persistence With EclipseLink

by shaunmsmith on Jun 29, 2009

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OSGi Persistence With EclipseLink — Presentation Transcript