OSGi is a module system and service platform that improves modularity in applications. It defines bundles that encapsulate code and dependencies, and uses services to connect bundles dynamically at runtime. OSGi provides benefits like dynamic updating of bundles, versioning of multiple component versions, reduced complexity, and a small footprint. Bundles are implemented using JAR files and manifests define their exported packages and services. The OSGi specification also defines the lifecycle of bundles. Tools like Bndtools and Apache Felix can be used to develop with OSGi.

2. OSGi – introduction to
application modularity
Marek Koniew
the most probable future of core+

3. What is OSGi
OSGi Alliance - Open Services Gateway Initiative
http://www.osgi.org
Membership $5000 - $25000 per year.
Latest specification version is 5 (no implementation yet).
Implementations:
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4. OSGi overview
 Bundles - OSGi components made by the developers.
 Services - connects bundles in a dynamic way.
 Modules - defines how a bundle can import and export code.
 Life-Cycle - to install, start, stop, update, and uninstall bundles.
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5. Modularity Benefits
What OSGi brings:
 Reuse – 3rd party components available as OSGi bundles
 Dynamic updates – bundle can be updated in runtime
 Adaptive – design forces to work when not everything is available
 Versioning – many component versions at the same time
 Simple – core API less than 30 classes/interfaces
 Small – OSGi v4 implementation is 300KB JAR
 Fast – working inside singe JVM – no serialization needed.
 Lazy – loading only what is necessary
 Reduced complexity – modules hides complexity from outside
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6. OSGi bundles
 Jar files
 Exporting packages : bundle definition
 Exporting services : runtime
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7. OSGi bundles – manifest.mf
Bundle-Activator: com.hybris.kernel.regioncache.osgi.OSGiBundleActivator
Bundle-Name: kernel-cache
Bundle-Version: 1.0.1
Export-Package: com.hybris.kernel.regioncache
Import-Package: com.hybris.commons.tenant,com.hybris.kernel.api;
version="[3.0,4)"
Private-Package: com.hybris.kernel.regioncache.counters,com.hybris.kerne
l.regioncache.impl,com.hybris.kernel.regioncache.jmx,com.hybris.kernel.
regioncache.osgi,com.hybris.kernel.regioncache.region
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8. OSGi bundles - versions
Transitive dependencies conflict is not a problem anymore:
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9. OSGi bundles - lifecycle
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GoGo shell

10. OSGi bundles - activator
public class OSGiBundleActivator implements org.osgi.framework.BundleActivator
{
@Override
public void start(final BundleContext context) throws Exception
{
System.out.println("Activating osgi module " +
context.getBundle().getSymbolicName());
}
@Override
public void stop(final BundleContext context) throws Exception
{
System.out.println("Stop " + context.getBundle().getSymbolicName());
}
}
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11. Whiteboard pattern
 Also applicable to configuration bundle.
 How it behavies when there is no service at the moment?
 Configuration can be provided this way.
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12. Semantic versioninig - definition
1.0.0.abc
Major.Minor.Micro.Qualifier
• Major: incompatible change for providers and
consumers
• Minor: incompatible change for providers
• Micro: compatible change
• Qualifier: anything (e.g. Build identity)
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13. Semantic versioninig - reference
 OSGI
http://www.osgi.org/wiki/uploads/Links/SemanticVersioning.pdf
 SemVer.org
http://semver.org/
 Eclipse
http://wiki.eclipse.org/Version_Numbering
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14. Semantic versioninig – version ranges
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15. Semantic versioninig – bundle hell
 Bundle hell
 Feature grouping
 Apache ACE
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16. OSGi tools (selection)
 Bndtools
 Import analysis
 Semantic versioning
 Integrated testing
 Apache Felix
 OSGi implementation
 Maven integration
 GoGo shell
 Apache ACE
 Manage and distribute components
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17. Bndtools
 Eclipse only
 Feature reach
 Import analysis
 Repositories
 OBR resolving (OSGi bundle repository)
 Semantic versioning
 Instant builder
 Integrated testing
 Live presentation
 Releasing and version control
 Calculated imports
 Integration tests
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18. OSGi testing
 Unit tests – use mocks
 Integration tests
 bndtools in eclipse
 bndtools ant task (also from maven)
 tycho-surefire maven plugin
 OSGi Assertion library
https://github.com/dpishchukhin/org.knowhowlab.osgi.testing
 assertServiceAvailable(CacheController.class)
 findBundle(„kernel-cache”).stop()
 …
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19. Maven integration
<packaging>bundle</packaging>
…
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<configuration>
<instructions>
<Export-Package>com.hybris.kernel.regioncache</Export-
Package>
<Private-Package>com.hybris.kernel.regioncache.*</Private-
Package>
<Bundle-Activator>
com.hybris.kernel.regioncache.osgi.OSGiBundleActivator
</Bundle-Activator>
<Import-Package>com.hybris.kernel.api</Import-Package>
</instructions>
</configuration>
</plugin>
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20. OSGi – DI
 Declarative services
http://wiki.osgi.org/wiki/Declarative_Services
 Blueprint
http://wiki.osgi.org/wiki/Blueprint
 CDI-OSGi (draft)
https://speakerdeck.com/paulbakker/rfc-193-osgi-cdi
• Hide OSGi service management complexity
• Still to implement manually situation when service is not available !!!
• Only singleton services supported. RFC-195 (draft) introduces prototype.
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21. OSGi – Declarative Services
 Functionality provided by OSGi 4 specification
package com.hybris;
import aQute.bnd.annotation.component.*;
@Component
Class Hello {
private Log log;
@Reference(unbind = „unSetLog”)
public void setLog(Log log) { … }
public void unSetLog(Log log) { … }
}
 Manifest.mf
Service-Component: com.hybris.*;
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22. OSGi – Blueprint
 Defined in OSGi v4.2
 Implemented
 Apache Aries
 Eclipse Gemini
 Spring DM (dead)
 Manifest.mf
Spring-Context: config/hello-context.xml; wait-for-dependencies:=true; timeout:=1000
 ServiceUnavailableException after timeout 19

23. OSGi – CDI (Contexts and Dependency Injection)
 Draft RFC-193 no implementation yet
 https://speakerdeck.com/paulbakker/rfc-193-osgi-cdi - Luminis Tech.
@OSGIComponent
public class MyComponent {
@Inject
@OSGiService(required=false)
MyService myService;
}
 Service dynamics
 Injection happens every time MyService is registered/deregistered
 With required=true MyCOmponent is deregistered when MyService is not
available
 Declarative service listeners @ServiceAdded, @ServiceRemoved
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24. Core+ cache as external module - motivation
15

25. Core+ cache as external module - overview
15
Embedded Felix. Separate Spring context. Service Proxy. Cache Client. API is a bundle.

26. Core+ cache as external module - demo
 Architecture
• embedded Felix OSGi container
• Spring context startup in bundle activator
• OSGi Service proxy – can act as proxy over any protocol
• Possibility to run without OSGi
• Cache checker
 Features
• No thigh coupling to OSGi
• Connect client to service without OSGi (direct spring)
• Incremental migration to OSGi
 Life demo
• Start/stop bundle
• How application reacts
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27. OSGi readings
Building Modular Cloud Apps with OSGi
Paul Bakker
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28. OSGi conference
 Never A Wrong (Semantic) Version Again! http://youtu.be/LBgNRsEJCWo
 DS, BP, EJB, CDI, WTF!? http://youtu.be/wr85daWNpZo
 Testing OSGi the "groovy" way http://youtu.be/UEWIoyIvT3Y
 Continuous Automated Deployment with Apache ACE
http://www.slideshare.net/mfrancis/continuous-automated-deployment-with-apache-ace-jago-de-
vreede-marcel-offermans
 More: http://www.osgi.org/CommunityEvent2013/Schedule
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29. Questions