Hibernate.orgCommunity Documentation
Abstract
The Open Services Gateway initiative (OSGi) specification describes a dynamic, modularized system. "Bundles" (components) can be installed, activated, deactivated, and uninstalled during runtime, without requiring a system restart. OSGi frameworks manage bundles' dependencies, packages, and classes. The framework is also in charge of ClassLoading, managing visibility of packages between bundles. Further, service registry and discovery is provided through a "whiteboard" pattern.
OSGi environments present numerous, unique challenges. Most notably, the dynamic nature of available bundles during runtime can require significant architectural considerations. Also, architectures must allow the OSGi-specific ClassLoading and service registration/discovery.
Table of Contents
Hibernate targets the OSGi 4.3 spec or later. It was necessary to start with 4.3, over 4.2, due to our
dependency on OSGi's BundleWiring for entity/mapping scanning.
Hibernate supports three types of configurations within OSGi.
Rather than embed OSGi capabilities into hibernate-core, hibernate-entitymanager, and sub-modules, hibernate-osgi was created. It's purposefully separated, isolating all OSGi dependencies. It provides an OSGi-specific ClassLoader (aggregates the container's CL with core and entitymanager CLs), JPA persistence provider, SF/EMF bootstrapping, entities/mappings scanner, and service management.
Apache Karaf environments tend to make heavy use of its "features" concept, where a feature is a set of order-specific
bundles focused on a concise capability. These features are typically defined in a features.xml file.
Hibernate produces and releases its own features.xml that defines a core hibernate-orm,
as well as additional features for optional functionality (caching, Envers, etc.).
This is included in the binary distribution, as well as deployed to the JBoss Nexus repository
(using the org.hibernate groupId and hibernate-osgi with the karaf.xml classifier).
Note that our features are versioned using the same ORM artifact versions they wrap. Also note that the features are heavily tested against Karaf 3.0.3 as a part of our PaxExam-based integration tests. However, they'll likely work on other versions as well.
hibernate-osgi, theoretically, supports a variety of OSGi containers, such as Equinox. In that case, please use features.xml as a reference for necessary bundles to activate and their correct ordering. However, note that Karaf starts a number of bundles automatically, several of which would need to be installed manually on alternatives.
All three configurations have a QuickStart/Demo available in the hibernate-demos project:
The Enterprise OSGi specification includes container-managed JPA. The container is responsible for
discovering persistence units in bundles and automatically creating the EntityManagerFactory (one EMF per PU).
It uses the JPA provider (hibernate-osgi) that has registered itself with the OSGi
PersistenceProvider service.
In order to utilize container-managed JPA, an Enterprise OSGi JPA container must be active in the runtime.
In Karaf, this means Aries JPA, which is included out-of-the-box (simply activate the jpa
and transaction features). Originally, we intended to include those dependencies within our own
features.xml. However, after guidance from the Karaf and Aries teams, it was pulled out.
This allows Hibernate OSGi to be portable and not be directly tied to Aries versions, instead having
the user choose which to use.
That being said, the QuickStart/Demo projects include a sample features.xml showing which features need activated in Karaf in order to support this environment. As mentioned, use this purely as a reference!
Similar to any other JPA setup, your bundle must include a persistence.xml file.
This is typically located in META-INF.
Typical Enterprise OSGi JPA usage includes a DataSource installed in the container. Your
bundle's persistence.xml calls out the DataSource through JNDI. For example, you could
install the following H2 DS. You can deploy the DS manually (Karaf has a deploy dir), or
through a "blueprint bundle" (blueprint:file:/[PATH]/datasource-h2.xml).
Example 18.1. datasource-h2.xml
<?xml version="1.0" encoding="UTF-8"?>
<!--
First install the H2 driver using:
> install -s mvn:com.h2database/h2/1.3.163
Then copy this file to the deploy folder
-->
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
<bean id="dataSource" class="org.h2.jdbcx.JdbcDataSource">
<property name="URL" value="jdbc:h2:mem:db1;DB_CLOSE_DELAY=-1;MVCC=TRUE"/>
<property name="user" value="sa"/>
<property name="password" value=""/>
</bean>
<service interface="javax.sql.DataSource" ref="dataSource">
<service-properties>
<entry key="osgi.jndi.service.name" value="jdbc/h2ds"/>
</service-properties>
</service>
</blueprint>
That DS is then used by your persistence.xml persistence-unit. The following works
in Karaf, but the names may need tweaked in alternative containers.
Example 18.2. META-INF/persistence.xml
<jta-data-source>osgi:service/javax.sql.DataSource/(osgi.jndi.service.name=jdbc/h2ds)</jta-data-source>
Your bundle's manifest will need to import, at a minimum,
javax.persistence
org.hibernate.proxy and javassist.util.proxy, due to
Hibernate's ability to return proxies for lazy initialization (Javassist enhancement
occurs on the entity's ClassLoader during runtime).
The easiest, and most supported, method of obtaining an EntityManager utilizes OSGi's
OSGI-INF/blueprint/blueprint.xml in your bundle. The container takes the name of your
persistence unit, then automatically injects
an EntityManager instance into your given bean attribute.
Example 18.3. OSGI-INF/blueprint/blueprint.xml
<?xml version="1.0" encoding="UTF-8"?>
<blueprint default-activation="eager"
xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
xmlns:jpa="http://aries.apache.org/xmlns/jpa/v1.0.0"
xmlns:tx="http://aries.apache.org/xmlns/transactions/v1.0.0">
<!-- This gets the container-managed EntityManager and injects it into the DataPointServiceImpl bean.
Assumes DataPointServiceImpl has an "entityManager" field with a getter and setter. -->
<bean id="dpService" class="org.hibernate.osgitest.DataPointServiceImpl">
<jpa:context unitname="managed-jpa" property="entityManager"/>
<tx:transaction method="*" value="Required"/>
</bean>
<service ref="dpService" interface="org.hibernate.osgitest.DataPointService" />
</blueprint>
Hibernate also supports the use of JPA through hibernate-entitymanager, unmanaged by the OSGi container. The client bundle is responsible for managing the EntityManagerFactory and EntityManagers.
Similar to any other JPA setup, your bundle must include a persistence.xml file.
This is typically located in META-INF.
Your bundle's manifest will need to import, at a minimum,
javax.persistence
org.hibernate.proxy and javassist.util.proxy, due to
Hibernate's ability to return proxies for lazy initialization (Javassist enhancement
occurs on the entity's ClassLoader during runtime)
JDBC driver package (example: org.h2)
org.osgi.framework, necessary to discover the EMF (described below)
hibernate-osgi registers an OSGi service, using the JPA PersistenceProvider interface
name, that bootstraps and creates an EntityManagerFactory specific for OSGi
environments. It is VITAL that your EMF be obtained through the service, rather than creating it
manually. The service handles the OSGi ClassLoader, discovered extension points, scanning, etc. Manually
creating an EntityManagerFactory is guaranteed to NOT work during runtime!
Example 18.4. Discover/Use EntityManagerFactory
public class HibernateUtil {
private EntityManagerFactory emf;
public EntityManager getEntityManager() {
return getEntityManagerFactory().createEntityManager();
}
private EntityManagerFactory getEntityManagerFactory() {
if ( emf == null ) {
Bundle thisBundle = FrameworkUtil.getBundle( HibernateUtil.class );
BundleContext context = thisBundle.getBundleContext();
ServiceReference serviceReference = context.getServiceReference( PersistenceProvider.class.getName() );
PersistenceProvider persistenceProvider = (PersistenceProvider) context.getService( serviceReference );
emf = persistenceProvider.createEntityManagerFactory( "YourPersistenceUnitName", null );
}
return emf;
}
}
Native Hibernate use is also supported. The client bundle is responsible for managing the SessionFactory and Sessions.
Your bundle's manifest will need to import, at a minimum,
javax.persistence
org.hibernate.proxy and javassist.util.proxy, due to
Hibernate's ability to return proxies for lazy initialization (Javassist enhancement
occurs on the entity's ClassLoader during runtime)
JDBC driver package (example: org.h2)
org.osgi.framework, necessary to discover the SF (described below)
org.hibernate.* packages, as necessary (ex: cfg, criterion, service, etc.)
hibernate-osgi registers an OSGi service, using the SessionFactory interface
name, that bootstraps and creates an SessionFactory specific for OSGi
environments. It is VITAL that your SF be obtained through the service, rather than creating it
manually. The service handles the OSGi ClassLoader, discovered extension points, scanning, etc. Manually
creating an SessionFactory is guaranteed to NOT work during runtime!
Example 18.5. Discover/Use EntityManagerFactory
public class HibernateUtil {
private SessionFactory sf;
public Session getSession() {
return getSessionFactory().openSession();
}
private SessionFactory getSessionFactory() {
if ( sf == null ) {
Bundle thisBundle = FrameworkUtil.getBundle( HibernateUtil.class );
BundleContext context = thisBundle.getBundleContext();
ServiceReference sr = context.getServiceReference( SessionFactory.class.getName() );
sf = (SessionFactory) context.getService( sr );
}
return sf;
}
}
The unmanaged-native demo project displays the use of optional Hibernate modules. Each module adds additional dependency bundles that must first be activated, either manually or through an additional feature. As of ORM 4.2, Envers is fully supported. Support for C3P0, Proxool, EhCache, and Infinispan were added in 4.3, however none of their 3rd party libraries currently work in OSGi (lots of ClassLoader problems, etc.). We're tracking the issues in JIRA.
Multiple contracts exist to allow applications to integrate with and extend Hibernate capabilities. Most
apps utilize JDK services to provide their implementations. hibernate-osgi supports the same
extensions through OSGi services. Implement and register them in any of the three configurations.
hibernate-osgi will discover and integrate them during EMF/SF bootstrapping. Supported extension points
are as follows. The specified interface should be used during service registration.
org.hibernate.integrator.spi.Integrator (as of 4.2)
org.hibernate.boot.registry.selector.StrategyRegistrationProvider (as of 4.3)
org.hibernate.boot.model.TypeContributor (as of 4.3)
javax.transaction.TransactionManager and
javax.transaction.UserTransaction (as of 4.2), however these are typically
provided by the OSGi container.
The easiest way to register extension point implementations is through a blueprint.xml
file. Add OSGI-INF/blueprint/blueprint.xml to your classpath. Envers' blueprint
is a great example:
Example 18.6. Example extension point registrations in blueprint.xml
<!-- ~ Hibernate, Relational Persistence for Idiomatic Java ~ ~ License: GNU Lesser General Public License (LGPL), version 2.1 or later. ~ See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>. --> <blueprint default-activation="eager" xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"> <bean id="integrator" class="org.hibernate.envers.boot.internal.EnversIntegrator" /> <service ref="integrator" interface="org.hibernate.integrator.spi.Integrator" /> <bean id="typeContributor" class="org.hibernate.envers.boot.internal.TypeContributorImpl" /> <service ref="typeContributor" interface="org.hibernate.boot.model.TypeContributor" /> </blueprint>
Extension points can also be registered programmatically with
BundleContext#registerService, typically within your
BundleActivator#start.
Technically, multiple persistence units are supported by Enterprise OSGi JPA and unmanaged Hibernate JPA use. However, we cannot currently support this in OSGi. In Hibernate 4, only one instance of the OSGi-specific ClassLoader is used per Hibernate bundle, mainly due to heavy use of static TCCL utilities. We hope to support one OSGi ClassLoader per persistence unit in Hibernate 5.
Scanning is supported to find non-explicitly listed entities and mappings. However, they MUST be in the same bundle as your persistence unit (fairly typical anyway). Our OSGi ClassLoader only considers the "requesting bundle" (hence the requirement on using services to create EMF/SF), rather than attempting to scan all available bundles. This is primarily for versioning considerations, collision protections, etc.
Some containers (ex: Aries) always return true for
PersistenceUnitInfo#excludeUnlistedClasses,
even if your persistence.xml explicitly has exclude-unlisted-classes set
to false. They claim it's to protect JPA providers from having to implement
scanning ("we handle it for you"), even though we still want to support it in many cases. The work
around is to set hibernate.archive.autodetection to, for example,
hbm,class. This tells hibernate to ignore the excludeUnlistedClasses value and
scan for *.hbm.xml and entities regardless.
Scanning does not currently support annotated packages on package-info.java.
Currently, Hibernate OSGi is primarily tested using Apache Karaf and Apache Aries JPA. Additional testing is needed with Equinox, Gemini, and other container providers.
Hibernate ORM has many dependencies that do not currently provide OSGi manifests.
The QuickStart tutorials make heavy use of 3rd party bundles (SpringSource, ServiceMix) or the
wrap:... operator.