The presentation was shared on Lviv JUG meeting #21

1. GETTING MODULARWITH OSGI

2. Agenda
› How to make my Java more modular
› Discover and exploit OSGI
› Tools, tools, tools…
› Output

3. About me
Who: Andrii Krokhmalnyi
Domain: Java/Java EE
Company: EPAM Systems
Experience in OSGI: about 2 years

5. Modular design
› Separates functionality into distinct isolated sections (modules)
› Defines a standard interface for modules
› Adds ability to replace modules transparently for users of the system
› Improves scalability and robustness of the system
› Makes functional parts of the system reusable and easily updatable
› …But adds some extent of complexity in overall system orchestration

6. Modularity in Java: Service Provider Interface
META-INF/services/com.foo.logging.LogRenderer
com.foo.logging.impl.ConsoleLogRenderer
com.foo.service.MyService.java
public static void main(String[] args) {
ServiceLoader<LogRenderer> renderers =
ServiceLoader.load(LogRenderer.class);
for (LogRenderer renderer : renderers) {
...
}

7. Modularity in Java: OSGI
MANIFEST.MF
META-INF/MANIFEST.MF
Manifest-Version: 1.0
Bundle-SymbolicName: foo-service
Bundle-Activator: com.foo.service.Activator
Export-Package: com.foo.dao,com.foo.domain,com.foo.service
Import-Package: com.foo.logging;version="[2.0,3)"
image from http://wallpapersus.com/

8. Project Jigsaw
src/main/java/com/foo/service/module-info.java
module foo-service @ 1.2 {
requires jdk.base;
requires optional jdk.jaxp;
exports com.foo.bar;
permits foo-ui;
permits foo-console;
class com.foo.service.Main;
view dao {
exports com.foo.dao;
}
}
image from http://wallpapersgroup.net/

10. History & versioning

11. OSGI specification (version 4.3)
Framework Specification
FrameworkAPI
Start LevelAPI
Remote
Services
Bundle
WiringAPI
Additional
Services
Specifications
Security Layer
Module Layer
Life Cycle Layer
Service Layer

12. Core :: Container and bundles
image from http://www.osgi.org
OSGI Container
Class Loader #1
Bundle #1
Class Loader #2
Bundle #2
Class Loader #N
Bundle #N
(modules)
a regular jar archive with tweaked manifest

13. Core :: Bundles life-cycle

14. Core :: MANIFEST.MF headers
foo-service.jar/META-INF/MANIFEST.MF
...
Bundle-ManifestVersion: 2
Bundle-SymbolicName: com.foo.service
Bundle-Name: Foo Service
Bundle-Description: Foo Service Module
Bundle-Version: 1.0
Bundle-Activator: com.foo.service.BundleActivator
Require-Bundle: com.foo.logging
Export-Package: com.foo.domain,com.foo.dao,com.foo.service;uses:=“org.apache.log4j”
Import-Package: com.foo.logging;version=“[1.0,2)”,org.apache.log4j;version=“[2.0,3)”
DynamicImport-Package: *
...

15. Core :: MANIFEST.MF and Maven
pom.xml
<build><plugins>
<plugin>
<groupId>org.apache.felix</groupId>
<artifactId>maven-bundle-plugin</artifactId>
<configuration>
<instructions>
<Bundle-Activator>com.foo.service.BundleActivator</Bundle-Activator>
<Export-Package>com.foo.service</Export-Package>
<Import-Package>
com.foo.domain,
com.foo.dao,
*
</Import-Package>
<DynamicImport-Package>*</DynamicImport-Package>
<Require-Bundle>org.apache.commons.io</Require-Bundle>
</instructions>
</configuration>
</plugin>
</plugins></build>

16. OSGI Services :: Service producer
ServiceProducerBundleActivator.java
public class ServiceProducerBundleActivator implements BundleActivator {
private ServiceRegistration registration;
public void start(BundleContext context) throws Exception {
registration = context.registerService(CustomService.class.getName(),
new CustomServiceImpl(), null);
}
public void stop(BundleContext context) throws Exception {
registration.unregister();
}
}

17. OSGI Services :: Service consumer
ServiceConsumerBundleActivator.java
public class ServiceConsumerBundleActivator implements BundleActivator {
public void start(BundleContext context) throws Exception {
ServiceReference ref =
context.getServiceReference(CustomService.class.getName());
CustomService customService = (CustomService) context.getService(ref);
customService.customMethod();
...
}
}

18. OSGI Services :: Spring version
/META-INF/spring/spring-osgi.xml
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="..."
xmlns:osgi="http://www.springframework.org/schema/osgi" xsi:schemaLocation="...">
<osgi:service ref="customService" interface="com.foo.service.CustomService"/>
</beans>
Producer
/META-INF/spring/spring-osgi.xml
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="..."
xmlns:osgi="http://www.springframework.org/schema/osgi" xsi:schemaLocation="...">
<osgi:reference id="customService" interface="com.foo.service.CustomService"/>
</beans>
Consumer

19. WhereWAR becomesWAB
foo-web.war/META-INF/MANIFEST.MF
...
Bundle-ManifestVersion: 2
Bundle-SymbolicName: com.foo.web
Bundle-Version: 1.0
Bundle-Activator: com.foo.web.BundleActivator
Web-ContextPath: mainapp/foo
Webapp-Context: mainapp/foo
Bundle-ClassPath: WEB-INF/classes,.
Import-Package: com.foo.service;version=“[1.0,2)”,
com.foo.logging;version=“[1.0,2)”;resolution:="optional"
...

20. Compendium services
Compendium
OSGI Services
Preferences UserAdmin Monitor Admin
Log HTTP
DeviceAccess
Configuration
Admin
… and many more

21. OSGI and unit testing
Spring
DM
MockBundle
MockBundleContext
MockServiceRegistrationMockServiceReference
MockBundleActivator

22. OSGI and integration testing
CustomServiceIntegrationTest.java
@RunWith(PaxExam.class)
@ExamReactorStrategy(PerMethod.class)
public class CustomServiceIntegrationTest {
@Inject
CustomService customService;
@Configuration
public Option[] config() {
return options(mavenBundle("com.foo", "foo-service", "1.0"), junitBundles());
}
}

24. BND
image from http://freemarket.kiev.ua/
Compiled
classes
Instruction
file
OSGI
bundle

25. OSGI containers/frameworks
Apache Felix
36%
Equinox
37%
SpringSource
dm Server
8%
Knopflerfish
8%
Concierge
8%
ProSyst
3%
OSGI CONTAINERS POPULARITY
(BYVOTES AT STACKOVERFLOW.COM)

26. Overview of Apache Felix
Apache License 2.0
OSGI R4.2 compatible
Provides a web console
Provides a Maven plugin
Active development
Proved solution
Good documentation

27. Overview of Apache Karaf
Apache License 2.0
Supports both Felix and Equinox
Lightweight and extensible
Interactive shell console
Hot deployment
Native OS integration
Extra management tools
Active development

28. OSGI in real world

30. Positives

31. Negatives