OSGi in 5 minutes
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The document provides an overview of OSGi, highlighting its features such as hot deployment, dependency management, and additional services. It explains the structure of an OSGi bundle and the role of the bundle activator, alongside its integration with Maven for dependency management. Two implementations of OSGi are mentioned: Eclipse Equinox and Apache Felix, noting their capabilities and uses.
OSGi in 5 minutes
- 2. Why ? • Most mature Java “plug‐in” technology • Allows hot deployment/un‐deployment • Manages dependencies between plug‐ins (aka OSGi bundles) • Offers (opKonal) addiKonal services (HTTP, configuraKon, etc...)
- 3. What is an OSGi Bundle ? JAR • Basically a JAR with: MANIFEST.MF –AddiKonal stuff in it’s Bundle-Name: Hello World manifest file Bundle-SymbolicName: org.example.helloworld Bundle-Description: A Hello World bundle Bundle-ManifestVersion: 2 Bundle-Version: 1.0.0 –A class called an Bundle-Activator: org.example.Activator Export-Package: org.example.helloworld;version="1.0.0" acKvator to register Import-Package: org.osgi.framework;version="1.3.0" services Classes –Your code and resources org.example.AcKvator ... –(OpKonally)Other JARs for legacy (migraKon) (OpKonal) JARs legacy‐1.0.jar purposes ...
- 4. OSGi Services Services are all implemented using one or more OSGi bundles Logging Component RunKme Wire Admin ConfiguraKon Admin Deployment Admin XML Parser Device Access Event Admin Measurement and State User Admin ApplicaKon Admin My Service 1 IO Connector HTTP Service My Service 2 Preferences UPnP Device Service
- 5. Bundle Activator • Simply iniKalizes and shuts down the package org.example; bundle (if needed) import org.osgi.framework.BundleActivator; import org.osgi.framework.BundleContext; public class Activator implements BundleActivator { • Can register with private BundleContext context; public void start(BundleContext context) throws Exception { System.out.println("Starting: Hello World"); exisKng services } this.context = context; public void stop(BundleContext context) throws Exception { • Helper classes are } System.out.println("Stopping: Goodbye Cruel World"); this.context = null; available to make } things easier
- 6. OSGi and Maven • Very good match as both know about dependencies • Maven project == OSGi bundle • Maven Felix Plugin does the packaging for you ! <plugin> <groupId>org.apache.felix</groupId> <artifactId>maven-bundle-plugin</artifactId> <extensions>true</extensions> <configuration> <instructions> <Export-Package>org.osgi.service.log</Export-Package> <Private-Package>org.apache.felix.log.impl</Private-Package> <Bundle-SymbolicName>${pom.artifactId}</Bundle-SymbolicName> <Bundle-Activator>${pom.artifactId}.impl.Activator</Bundle-Activator> <Export- Service>org.osgi.service.log.LogService,org.osgi.service.log.LogReaderService</ Export-Service> </instructions> </configuration> </plugin>
- 7. Learn more... • OSGi implementaKons –Eclipse Equinox : hfp://eclipse.org/equinox/ (most mature, was born out of Eclipse, integrated in Websphere and Eclipse) –Apache Felix : hfp://felix.apache.org (best integraKon with Maven, evolving rapidly, used in Apache Sling and other Apache projects