HHH-8112 osgi devguide
This commit is contained in:
Brett Meyer
Brett Meyer
parent
8f07d59243
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<surname>Badner</surname>
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</personname>
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</author>
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<author>
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<personname>
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<firstname>Brett</firstname>
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<surname>Meyer</surname>
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</personname>
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</author>
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<othercredit>
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<personname>
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@ -52,6 +52,7 @@
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<xi:include href="JMX.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<xi:include href="Envers.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<xi:include href="chapters/multitenancy/Multi_Tenancy.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<xi:include href="chapters/osgi/OSGi.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<xi:include href="appendix-Configuration_Properties.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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<xi:include href="appendices/legacy_criteria/Legacy_Criteria.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
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</book>
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@ -0,0 +1,402 @@
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<?xml version='1.0' encoding='utf-8'?>
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<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xl="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<info>
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<title>OSGi</title>
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<abstract>
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<para>
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The Open Services Gateway initiative (OSGi) specification describes a dynamic, modularized system. "Bundles"
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(components) can be installed, activated, deactivated, and uninstalled during runtime, without requiring
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a system restart. OSGi frameworks manage bundles' dependencies, packages, and classes. The framework
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is also in charge of ClassLoading, managing visibility of packages between bundles. Further, service
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registry and discovery is provided through a "whiteboard" pattern.
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</para>
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<para>
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OSGi environments present numerous, unique challenges. Most notably, the dynamic nature of available
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bundles during runtime can require significant architectural considerations. Also,
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architectures must allow the OSGi-specific ClassLoading and service registration/discovery.
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</para>
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</abstract>
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</info>
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<section>
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<title>OSGi Specification and Environment</title>
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<para>
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Hibernate targets the OSGi 4.3 spec or later. It was necessary to start with 4.3, over 4.2, due to our
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dependency on OSGi's <literal>BundleWiring</literal> for entity/mapping scanning.
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</para>
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<para>
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Hibernate supports three types of configurations within OSGi.
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<orderedlist>
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<listitem>
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<firstterm>Container-Managed JPA</firstterm>: <xref linkend="osgi-managed-jpa"/>
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</listitem>
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<listitem>
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<firstterm>Unmanaged JPA</firstterm>: <xref linkend="osgi-unmanaged-jpa"/>
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</listitem>
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<listitem>
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<firstterm>Unmanaged Native</firstterm>: <xref linkend="osgi-unmanaged-native"/>
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</listitem>
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</orderedlist>
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</para>
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</section>
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<section>
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<title>hibernate-osgi</title>
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<para>
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Rather than embed OSGi capabilities into hibernate-core, hibernate-entitymanager, and sub-modules,
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hibernate-osgi was created. It's purposefully separated, isolating all OSGi dependencies. It provides an
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OSGi-specific ClassLoader (aggregates the container's CL with core and entitymanager CLs), JPA persistence
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provider, SF/EMF bootstrapping, entities/mappings scanner, and service management.
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</para>
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</section>
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<section xml:id="osgi-managed-jpa">
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<title>Container-Managed JPA</title>
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<para>
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The Enterprise OSGi specification includes container-managed JPA. The container is responsible for
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discovering persistence units and creating the <literal>EntityManagerFactory</literal> (one EMF per PU).
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It uses the JPA provider (hibernate-osgi) that has registered itself with the OSGi
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<literal>PersistenceProvider</literal> service.
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</para>
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<para>
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Quickstart tutorial project, demonstrating a container-managed JPA client bundle:
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<link xl:href="https://github.com/hibernate/hibernate-orm/tree/master/documentation/src/main/docbook/quickstart/tutorials/osgi/managed-jpa">managed-jpa</link>
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</para>
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<section>
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<title>Client bundle imports</title>
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<para>
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Your client bundle's manifest will need to import, at a minimum,
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<itemizedlist>
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<listitem>
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<literal>javax.persistence</literal>
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</listitem>
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<listitem>
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<para>
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<literal>org.hibernate.proxy</literal> and <literal>javassist.util.proxy</literal>, due to
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Hibernate's ability to return proxies for lazy initialization
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</section>
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<section>
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<title>JPA 2.1</title>
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<para>
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No Enterprise OSGi JPA container currently supports JPA 2.1 (the spec is not yet released). For
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testing, the managed-jpa example makes use of
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<link xl:href="https://github.com/brmeyer/aries/tree/jpa21">Brett's fork of Aries</link>. To work
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with Hibernate 4.3, clone the fork and build Aries JPA.
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</para>
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</section>
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<section>
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<title>DataSource</title>
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<para>
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Typical Enterprise OSGi JPA usage includes a DataSource installed in the container. The client
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bundle's <literal>persistence.xml</literal> uses the DataSource through JNDI. For an example,
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see the QuickStart's DataSource:
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/datasource-h2.xml">datasource-h2.xml</link>
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The DataSource is then called out in
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/managed-jpa/src/main/resources/META-INF/persistence.xml">
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persistence.xml's</link> <literal>jta-data-source</literal>.
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</para>
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</section>
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<section>
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<title>Bundle Ordering</title>
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<para>
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Hibernate currently requires fairly specific bundle activation ordering. See the managed-jpa
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QuickStart's
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/managed-jpa/features.xml">features.xml</link>
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for the best supported sequence.
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</para>
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</section>
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<section>
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<title>Obtaining an EntityManger</title>
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<para>
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The easiest, and most supported, method of obtaining an <literal>EntityManager</literal> utilizes OSGi's
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<literal>blueprint.xml</literal>. The container takes the name of your persistence unit, then injects
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an <literal>EntityManager</literal> instance into your given bean attribute. See the
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<literal>dpService</literal> bean in the managed-jpa QuickStart's
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/managed-jpa/src/main/resources/OSGI-INF/blueprint/blueprint.xml">blueprint.xml</link>
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for an example.
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</para>
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</section>
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</section>
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<section xml:id="osgi-unmanaged-jpa">
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<title>Unmanaged JPA</title>
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<para>
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Hibernate also supports the use of JPA through hibernate-entitymanager, unmanaged by the OSGi
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container. The client bundle is responsible for managing the EntityManagerFactory and EntityManagers.
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</para>
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<para>
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Quickstart tutorial project, demonstrating an unmanaged JPA client bundle:
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<link xl:href="https://github.com/hibernate/hibernate-orm/tree/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-jpa">unmanaged-jpa</link>
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</para>
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<section>
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<title>Client bundle imports</title>
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<para>
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Your client bundle's manifest will need to import, at a minimum,
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<itemizedlist>
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<listitem>
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<literal>javax.persistence</literal>
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</listitem>
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<listitem>
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<para>
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<literal>org.hibernate.proxy</literal> and <literal>javassist.util.proxy</literal>, due to
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Hibernate's ability to return proxies for lazy initialization
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</para>
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</listitem>
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<listitem>
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<para>
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JDBC driver package (example: <literal>org.h2</literal>)
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>org.osgi.framework</literal>, necessary to discover the EMF (described below)
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</section>
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<section>
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<title>Bundle Ordering</title>
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<para>
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Hibernate currently requires fairly specific bundle activation ordering. See the unmanaged-jpa
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QuickStart's
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-jpa/features.xml">features.xml</link>
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for the best supported sequence.
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</para>
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</section>
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<section>
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<title>Obtaining an EntityMangerFactory</title>
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<para>
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hibernate-osgi registers an OSGi service, using the JPA <literal>PersistenceProvider</literal> interface
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name, that bootstraps and creates an <literal>EntityManagerFactory</literal> specific for OSGi
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environments. It is VITAL that your EMF be obtained through the service, rather than creating it
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manually. The service handles the OSGi ClassLoader, discovered extension points, scanning, etc. Manually
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creating an <literal>EntityManagerFactory</literal> is guaranteed to NOT work during runtime!
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</para>
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<para>
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For an example on how to discover and use the service, see the unmanaged-jpa
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QuickStart's
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-jpa/src/main/java/org/hibernate/osgitest/HibernateUtil.java">HibernateUtil.java</link>.
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</para>
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</section>
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</section>
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<section xml:id="osgi-unmanaged-native">
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<title>Unmanaged Native</title>
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<para>
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Native Hibernate use is also supported. The client bundle is responsible for managing the
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SessionFactory and Sessions.
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</para>
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<para>
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Quickstart tutorial project, demonstrating an unmanaged native client bundle:
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<link xl:href="https://github.com/hibernate/hibernate-orm/tree/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-native">unmanaged-native</link>
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</para>
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<section>
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<title>Client bundle imports</title>
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<para>
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Your client bundle's manifest will need to import, at a minimum,
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<itemizedlist>
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<listitem>
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<literal>javax.persistence</literal>
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</listitem>
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<listitem>
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<para>
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<literal>org.hibernate.proxy</literal> and <literal>javassist.util.proxy</literal>, due to
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Hibernate's ability to return proxies for lazy initialization
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</para>
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</listitem>
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<listitem>
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<para>
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JDBC driver package (example: <literal>org.h2</literal>)
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>org.osgi.framework</literal>, necessary to discover the SF (described below)
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</para>
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</listitem>
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<listitem>
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<para>
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<literal>org.hibernate.*</literal> packages, as necessary (ex: cfg, criterion, service, etc.)
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</section>
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<section>
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<title>Bundle Ordering</title>
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<para>
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Hibernate currently requires fairly specific bundle activation ordering. See the unmanaged-native
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QuickStart's
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-native/features.xml">features.xml</link>
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for the best supported sequence.
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</para>
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</section>
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<section>
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<title>Obtaining an SessionFactory</title>
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<para>
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hibernate-osgi registers an OSGi service, using the <literal>SessionFactory</literal> interface
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name, that bootstraps and creates an <literal>SessionFactory</literal> specific for OSGi
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environments. It is VITAL that your SF be obtained through the service, rather than creating it
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manually. The service handles the OSGi ClassLoader, discovered extension points, scanning, etc. Manually
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creating an <literal>SessionFactory</literal> is guaranteed to NOT work during runtime!
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</para>
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<para>
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For an example on how to discover and use the service, see the unmanaged-native
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QuickStart's
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<link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-native/src/main/java/org/hibernate/osgitest/HibernateUtil.java">HibernateUtil.java</link>.
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</para>
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</section>
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</section>
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<section>
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<title>Optional Modules</title>
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<para>
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The <link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-native">unmanaged-native</link>
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QuickStart project demonstrates the use of optional Hibernate modules. Each module adds additional
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dependency bundles that must first be activated
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(see <link xl:href="https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/unmanaged-native/features.xml">features.xml</link>).
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As of ORM 4.2, Envers is fully supported. Support for C3P0, Proxool, EhCache, and Infinispan were added in
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4.3, however none of their 3rd party libraries currently work in OSGi (lots of ClassLoader problems, etc.).
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We're tracking the issues in JIRA.
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</para>
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</section>
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<section>
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<title>Extension Points</title>
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<para>
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Multiple contracts exist to allow applications to integrate with and extend Hibernate capabilities. Most
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apps utilize JDK services to provide their implementations. hibernate-osgi supports the same
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extensions through OSGi services. Implement and register them in any of the three configurations.
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hibernate-osgi will discover and integrate them during EMF/SF bootstrapping. Supported extension points
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are as follows. The specified interface should be used during service registration.
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<itemizedlist>
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<listitem>
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<literal>org.hibernate.integrator.spi.Integrator</literal> (as of 4.2)
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</listitem>
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<listitem>
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<literal>org.hibernate.boot.registry.selector.StrategyRegistrationProvider</literal> (as of 4.3)
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</listitem>
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<listitem>
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<literal>org.hibernate.metamodel.spi.TypeContributor</literal> (as of 4.3)
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</listitem>
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<listitem>
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JTA's <literal>javax.transaction.TransactionManager</literal> and
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<literal>javax.transaction.UserTransaction</literal> (as of 4.2), however these are typically
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provided by the OSGi container.
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</listitem>
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</itemizedlist>
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</para>
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<para>
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The easiest way to register extension point implementations is through a <literal>blueprint.xml</literal>
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file. Add <literal>OSGI-INF/blueprint/blueprint.xml</literal> to your classpath. Envers' blueprint
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is a great example:
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</para>
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<example>
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<title>Example extension point registrations in blueprint.xml</title>
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<programlisting role="XML"><xi:include href="extras/extension_point_blueprint.xml" parse="text"/></programlisting>
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</example>
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<para>
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Extension points can also be registered programmatically with
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<literal>BundleContext#registerService</literal>, typically within your
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<literal>BundleActivator#start</literal>.
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</para>
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</section>
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<section>
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<title>Caveats</title>
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<itemizedlist>
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<listitem>
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<para>
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Technically, multiple persistence units are supported by Enterprise OSGi JPA and unmanaged
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Hibernate JPA use. However, we cannot currently support this in OSGi. In Hibernate 4, only one
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instance of the OSGi-specific ClassLoader is used per Hibernate bundle, mainly due to heavy use of
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static TCCL utilities. We hope to support one OSGi ClassLoader per persistence unit in
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Hibernate 5.
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</para>
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</listitem>
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<listitem>
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<para>
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Scanning is supported to find non-explicitly listed entities and mappings. However, they MUST be
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in the same bundle as your persistence unit (fairly typical anyway). Our OSGi ClassLoader only
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considers the "requesting bundle" (hence the requirement on using services to create EMF/SF),
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rather than attempting to scan all available bundles. This is primarily for versioning
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considerations, collision protections, etc.
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</para>
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</listitem>
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<listitem>
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<para>
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Currently, Hibernate OSGi is primarily tested using Apache Karaf and Apache Aries JPA. Additional
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testing is needed with Equinox, Gemini, and other container providers.
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</para>
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</listitem>
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<listitem>
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<para>
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Hibernate ORM has many dependencies that do not currently provide OSGi manifests.
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The QuickStart tutorials make heavy use of 3rd party bundles (SpringSource, ServiceMix) or the
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<literal>wrap:...</literal> operator.
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</para>
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</listitem>
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<listitem>
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<para>
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As previously mentioned, bundle activation is currently order specific. See the QuickStart
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tutorials' <literal>features.xml</literal> for example sequences.
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</para>
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</listitem>
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<listitem>
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<para>
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The environment should be considered STATIC. Hibernate currently does not support the ability
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to dynamically add and remove client bundles during runtime. Doing so is typically
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catastrophic. We hope to better support at least partially-dynamic environments in
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Hibernate 5.
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</para>
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</listitem>
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<listitem>
|
||||
<para>
|
||||
No Enterprise OSGi JPA container currently supports JPA 2.1 (the spec is not yet released). For
|
||||
testing, the managed-jpa example makes use of
|
||||
<link xl:href="https://github.com/brmeyer/aries/tree/jpa21">Brett's fork of Aries</link>. To work
|
||||
with Hibernate 4.3, clone the fork and build Aries JPA.
|
||||
</para>
|
||||
</listitem>
|
||||
</itemizedlist>
|
||||
</section>
|
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|
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</chapter>
|
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|
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@ -0,0 +1,11 @@
|
|||
<blueprint default-activation="eager"
|
||||
xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
|
||||
|
||||
<bean id="integrator" class="org.hibernate.envers.event.spi.EnversIntegrator" />
|
||||
<service ref="integrator" interface="org.hibernate.integrator.spi.Integrator" />
|
||||
|
||||
<bean id="typeContributor"
|
||||
class="org.hibernate.envers.internal.entities.TypeContributorImpl" />
|
||||
<service ref="typeContributor" interface="org.hibernate.metamodel.spi.TypeContributor" />
|
||||
|
||||
</blueprint>
|
||||
Loading…
Reference in New Issue