The JBoss Application Server JPA subsystem implements the JPA 2.0 container-managed requirements. Deploys the persistence unit definitions, the persistence unit/context annotations and persistence unit/context references in the deployment descriptor. JPA Applications use the Hibernate (core) 4.0 persistence provider, that is included with JBoss AS. The JPA subsystem uses the standard SPI (javax.persistence.spi.PersistenceProvider) to access the Hibernate persistence provider and some additional extensions as well.
During application deployment, JPA use is detected (e.g. persistence.xml or @PersistenceContext/Unit annotations) and injects Hibernate dependencies into the application deployment. This makes it easy to deploy JPA applications.
In the remainder of this documentation, ”entity manager” refers to an instance of the javax.persistence.EntityManager class. Javadoc for the JPA interfaces http://download.oracle.com/javaee/6/api/javax/persistence/package-summary.html and JPA 2.0 specification. The Hibernate documentation (work in progress) will describe the JPA 2.0 entity manager in greater detail (devguide will be here).
The entity manager is similar to the Hibernate Session class; applications use it to create/read/update/delete data (and related operations). Applications can use application-managed or container-managed entity managers. Keep in mind that the entity manager is not expected to be thread safe (don't inject it into a servlet class variable which is visible to multiple threads).
Application-managed entity managers provide direct access to the underlying persistence provider (org.hibernate.ejb.HibernatePersistence). The scope of the application-managed entity manager is from when the application creates it and lasts until the app closes it. Use the @PersistenceUnit annotation to inject a persistence unit into a javax.persistence.EntityManagerFactory. The EntityManagerFactory can return an application-managed entity manager.
Container-managed entity managers auto-magically manage the underlying persistence provider for the application. Container-managed entity managers may use transaction-scoped persistence contexts or extended persistence contexts. The container-managed entity manager will create instances of the underlying persistence provider as needed. Every time that a new underlying persistence provider (org.hibernate.ejb.HibernatePersistence) instance is created, a new persistence context is also created (as an implementation detail of the underlying persistence provider).
The JPA persistence context contains the entities managed by the persistence provider. The persistence context acts like a first level (transactional) cache for interacting with the datasource. Loaded entities are placed into the persistence context before being returned to the application. Entities changes are also placed into the persistence context (to be saved in the database when the transaction commits).
The transaction-scoped persistence context coordinates with the (active) JTA transaction. When the transaction commits, the persistence context is flushed to the datasource (entity objects are detached but may still be referenced by application code). All entity changes that are expected to be saved to the datasource, must be made during a transaction. Entities read outside of a transaction will be detached immediately (since there is no transaction to coordinate with). Example transaction-scoped persistence context is below.
The Container-managed extended persistence context can span multiple transactions and allows data modifications to be queued up (like a shopping cart), without an active JTA transaction (to be applied during the next JTA TX). The Container-managed extended persistence context can only be injected into a stateful session bean.
JPA 2.0 makes it easy to use your (pojo) plain old Java class to represent a database table row.
The entity lifecycle is managed by the underlying persistence provider.
- New (transient): an entity is new if it has just been instantiated using the new operator, and it is not associated with a persistence context. It has no persistent representation in the database and no identifier value has been assigned.
- Managed (persistent): a managed entity instance is an instance with a persistent identity that is currently associated with a persistence context.
- Detached: the entity instance is an instance with a persistent identity that is no longer associated with a persistence context, usually because the persistence context was closed or the instance was evicted from the context.
- Removed: a removed entity instance is an instance with a persistent identity, associated with a persistence context, but scheduled for removal from the database.
The persistence.xml contains the persistence unit configuration (e.g. datasource name) and as described in the JPA 2.0 spec (section 8.2), the jar file or directory whose META-INF directory contains the persistence.xml file is termed the root of the persistence unit. In Java EE environments, the root of a persistence unit must be one of the following:
- an EJB-JAR file
- the WEB-INF/classes directory of a WAR file
- a jar file in the WEB-INF/lib directory of a WAR file
- a jar file in the EAR library directory
- an application client jar file
The persistence.xml can specify either a JTA datasource or a non-JTA datasource. The JTA datasource is expected to be used within the EE environment (even when reading data without an active transaction). If a datasource is not specified, the default-datasource will instead be used (must be configured).
The “org.jboss.as.jpa” logging can be enabled to get the following information:
- INFO - when persistence.xml has been parsed, starting of persistence unit service (per deployed persistence.xml), stopping of persistence unit service
- DEBUG - informs about entity managers being injected, creating/reusing transaction scoped entity manager for active transaction
- TRACE - shows how long each entity manager operation took in milliseconds, application searches for a persistence unit, parsing of persistence.xml
To enable TRACE, open the as/standalone/configuration/standalone.xml (or as/domain/configuration/domain.xml) file. Search for <subsystem xmlns="urn:jboss:domain:logging:1.0"> and add the org.jboss.as.jpa category :
Hibernate 4 is packaged with the AS and is the default persistence provider.
AS 7.0.1 allows the packaging of Hibernate 3.5 (or greater) persistence provider jars with the application. The JPA deployer will detect the presence of a persistence provider in the application and jboss.as.jpa.providerModule needs to be set to hibernate3-bundled.
The AS7 testsuite contains a test that packages jars from the Hibernate 3.6.5.Final jars (hibernate3-core.jar, hibernate3-commons-annotations.jar, hibernate3-entitymanager.jar, dom4j.jar, slf4j.jar, slf4j-api.jar, commons-collections.jar, antlr.jar) in the ear lib.
Applications can share the same Hibernate3 (for Hibernate 3.5 or greater) persistence provider by manually creating an org.hibernate:3 module (in the AS/modules folder). Steps to create the Hibernate3 module:
- In a command shell, go to the AS installation and change into the modules/org folder.
cd AS/modules/org or cd AS\modules\org\hibernate
- Create folder for slot 3 to hold Hibernate 3
- Copy the Hibernate3 jars into this new AS/modules/org/hibernate/3 folder
(hibernate3-core.jar, hibernate3-commons-annotations.jar, hibernate3-entitymanager.jar, dom4j.jar, slf4j.jar, slf4j-api.jar, commons-collections.jar, antlr.jar, slf4j-api.jar, commons-collections.jar, antlr.jar and any other jar needed for Hibernate 3).
- Create the AS/modules/org/hibernate/3/module.xml file with contents:
In your persistence.xml, you will refer to the Hibernate 3 persistence provider as follows:
This is a work in progress. A project to build integration for persistence providers like EclipseLink, is here. It looks like help from the EclipseLink community, would be helpful (in adding AS7 support to EclipseLink or suggesting how existing builds of EclipseLink could be used). EclipseLink contains integration classes for each of the different runtime environments (like earlier versions of JBoss AS). We also need to fix the AS7 persistence unit temp class path.
Integration code for other persistence providers can also be added to the jpa-modules project. Note that the project is in its very early stages and you need to build AS7 locally on the same machine (so that the snapshot versions of the AS7 JPA SPI jars will be available). Also note that the AS7 JPA SPI is likely to evolve a bit as we add additional integration modules. It will stabilize more when we have integrated persistence providers from three different sources (We already have Hibernate integrated, so that is one of three needed).
If your interested in helping integrate AS7 with other persistence providers, please find Scott Marlow on IRC (irc://irc.freenode.org/jboss-as7) or send email to .
Applications that use the Hibernate API directly, are referred to here as native Hibernate applications. Native Hibernate applications, can choose to use the Hibernate jars included with JBoss AS or they can package their own copy of the Hibernate jars. Applications that utilize JPA will automatically have the JBoss AS Hibernate injected onto the application deployment classpath. Meaning that JPA applications, should expect to use the Hibernate jars included in JBoss AS.
Example MANIFEST.MF entry to add Hibernate dependency:
You can inject a org.hibernate.Session and org.hibernate.SessionFactory directly, just as you can do with EntityManagers and EntityManagerFactorys.
The following properties are supported in the persistence unit definition (in the persistence.xml file):
|jboss.as.jpa.providerModule||is the name of the persistence provider module (default is org.hibernate). Should be hibernate3-bundled if Hibernate 3 jars are in the application archive (adapterModule and adapterClass will automatically be set for hibernate3-bundled).|
|jboss.as.jpa.adapterModule||is the name of the integration classes that help the AS to work with the persistence provider. Current valid values are org.jboss.as.jpa.hibernate:4 (Hibernate 4 integration classes) and org.jboss.as.jpa.hibernate:3 (Hibernate 3 integration classes). Other integration adapter modules are expected to be added.|
|jboss.as.jpa.adapterClass||is the class name of the integration adapter. Current valid values are org.jboss.as.jpa.hibernate3.HibernatePersistenceProviderAdaptor and org.jboss.as.jpa.hibernate4.HibernatePersistenceProviderAdaptor.|
Many thanks to the community, for reporting issues, solutions and code changes. A number of people have been answering AS7 forum questions related to JPA usage. I would like to thank them for this, as well as those reporting issues. For those of you that haven't downloaded the AS source code and started hacking patches together. I would like to encourage you to start by reading Hacking on AS7. You will find that it easy very easy to find your way around the AS7/JPA/* source tree and make changes. The following list of contributors should grow over time, I hope to see more of you listed here.
- Steve Ebersole (lead of the Hibernate project)
- Stuart Douglas (lead of the Seam Persistence project, AS7 project team member/committer)
- Jaikiran Pai (Active member of JBoss forums and JBoss EJB3 project team member)
- Strong Liu (leads the productization effort of Hibernate in the EAP product)
- Scott Marlow (lead of the AS7 JPA sub-project)
- Prasad Deshpande has reported issues but more importantly, has been answering others JPA related questions as well.
If you see someone answering JPA related questions in the forums,or if I left you out (and you have been answering JPA questions), add the name to the above list.