Евгений Капинос "Advanced JPA (Java Persistent API)"

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Advanced
Java Persistence API
Evgeniy Kapinos

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What is Java Persistence API ?
JPA - is the specification of the Java API for the management of
persistence and object/relational mapping

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JPA related technologies
EJB
with CMP
EJB 3.0
JPA
1.0 JPA 2.0 JPA 2.1
JDO JDO 2.0
Hibernate
Hibernate
3.2
EE
EE, SE
EE, SE
JSR-
220
JSR-
317
JSR-
338
JSR-
243
2010
2008
1997
2004
JSR-19, JSR-153
JSR-12
2001
Vendors
• Hibernate 3.5
• EclipseLink
• DataNucleus
• Batoo JPA
• Kundera
• ObjectDB
• OpenJPA
• OrientDB
• WebSphere
2007
2009 2013
Vendors
• Hibernate 4.3
• EclipseLink
• DataNucleus
Lightweightalternativeof

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How JPA specification has been created ?
 Java Community Process (JCP) established since 1998
- Java Specification Request (JSR)
 Specification: JSR 338: Java™ Persistence API, Version 2.1
 Reference implementation: EclipseLink 2.5.0
 Technology Compatibility Kit: test suite

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Architecture
Entity Manager
Factory
Entity Manager
Persistence
Context
(L1 cache)
Transaction Database
Connection and
mapping
metadata
Entity
Shared cache
(L2 cache)

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Entity
 Starting point: object/relational mapping
- Annotations or XML descriptor
- Syntax - just Google it
- Java to DDL (vise versa) generation
 Result: Java classes, database schema and
mapping meta information

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Entity Manager Factory
 Configuring “persistance.xml” parameters:
- Required: Persistent-Unit name only
- Optional: DB connection parameters, transaction type, mapping
metadata (XML, root jar, list of Classes), persistency-provider properties
 Result: Entity Manager Factory ready for persistence
Entity Manager
Factory
Connection and
mapping
metadata

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Entity Manager & Persistent Context
 Entity manager
- Used by Developer. Manages Entity live-circle (CRUD), JPQL, etc.
- Created by Entity Manager Factory
- Interacts with transactions (create / join)
- Entity keep is delegated to Persistent Context
 SQL Read on demand, but Persistent Context
 SQL Write on “flush()” call
- Session scope, not thread-safe
Entity Manager
Persistence
Context
Entity
Entity Manager
Factory
 Persistent Context
- Accessible by Entity Manager ‘s only
- L1 cache. Identity Set (search with ‘’==“)
- Produces REPETABLE_READ behavior
Transaction

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Entity Manager – create & delete operations
Search in
Persistence Context by
“==“
no equals()/hashCode()
required

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Entity Manager – read operations
REPETABLE_READ
em.find() & JPQL

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Entity Manager – update operation
Dirty check – depends on persistent-provider.
No equals()/hashCode() required.
E.g. Hibernate uses “inspection” strategy by default

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Entity Manager – transaction types
 JPA supports two transaction types
- RESOURSE_LOCAL – transactions created and controlled
by Entity Manager (Java SE & Java EE).
- JTA – transactions created and controlled by Container
(Java EE, JSR-907). Default value.
 Transaction type is defined in “percistance.xml”
- Entity Manager Factory creates Entity Managers
configured for one and only one transaction type
- Simultaneous work with two transaction types is not
supported within one Entity Manager Factory
 Partly transparent for Developer
Entity Manager
Entity Manager
Factory
Resource-local
Entity Manager
JTA
Entity Manager

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Resource-local Entity Manager
Resource-local
Entity Manager
Persistence
Context
Entity Manager
Factory
Entity
Transaction

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EJB
JTA Entity Manager (stateless EJB example)
JTA
Entity Manager
Transactional
Persistence
Context
Entity Manager
Factory
Container JTA transaction
EJB
JTA
Entity Manager

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