This is an introductory session to OSGi which I did during the Colombo Java Meetup on 24th of Jan, 2013

1. Demystifying OSGi
Colombo Java Meetup
24-01-2013
Sameera Jayasoma Pradeep Fernando
WSO2 Inc. WSO2 Inc.

2. Modular Systems...

3. Image courtsy of: http://www.thefeltsource.com/Human-Anatomy.html

4. Down the Memory Lane...

5. Functions
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

6. Modules
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

7. Classes/Objects
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

8. Packages
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

9. Modularity with Java
Can we build a pure modular system with Java?

10. Modularity with Java
● Yes we can...
○ Various Java libraries and Plugin systems.
○ Eclipse IDE plugins
○ IntelliJIDEA plugins.
● But...

11. Modularity with Java
What are the limitations?
● No standard way of building a modular system.
○ Class loader based techniques.
● Runtime Vs Compile time difference.
○ Flat, single classpath.
● No model for sharing of resource at runtime.

12. Runtime vs Compile time.
log4j-2.1.0.jar
axis2-kernel-1
.6.0.jar axiom
-3.3.0.ja r jdom.1.0.jar
spring-core.1
.0.jar
saxon-8.9.0.ja
r poi-3.5.0.jar
wss4j-1.5.11.
jar quart-1.1.0.ja
r woden-1.0.0.ja
r
cindy-5.7.0.ja
r rampart-2.3.0
.ja r derby-10.3.0.ja
r bcel-5.2.0.jar
jaxb-2.2.5.jar
Java application. Compile time view

13. Runtime vs Compile time
log4j-2.1.0.jar
wss4j-1.5.11.jar
axis2-kernel-1.6.0
.jar quart-1.1.0.ja
r
axiom-3.3.0.jar
woden-1.0.0.jar
jdom.1.0.jar
cindy-5.7.0.jar
spring-core.1.0.ja
r rampart-2.3.0.jar
saxon-8.9.0.jar
derby-10.3.0.jar
Single linear poi-3.5.0.jar
bcel-5.2.0.jar
classpath. jaxb-2.2.5.jar
Runtime classloading architecture.

14. Multiple Library Versions
log4j-2.1.0.jar
wss4j-1.5.11.jar
axis2-kernel-1.6.0
.jar quart-1.1.0.jar
axiom-3.3.0.jar
woden-1.0.0.jar
jdom.1.0.jar
cindy-5.7.0.jar
spring-core.1.0.ja
r rampart-2.3.0.jar
saxon-8.9.0.jar
derby-10.3.0.jar
poi-3.5.0.jar
Single linear bcel-5.2.0.jar
jaxb-2.2.5.jar
classpath. log4j-3.0.0.jar
Can we achieve this in Java?

15. Tight Coupling among modules
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

16. What Next?
● How do we overcome those limitations in Java?
● We were discussing functions, module, objects and
packages.
● What next???

17. What Next???
● How about an abstraction where you can work at the
package level as opposed to class/object level?
○ Importing packages.
○ Exporting packages.
○ A way to have private packages.
● Can we achieve the limitations that we discussed in
Java from this model?

18. Next Level of Modularity
? What next?
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

19. Next Level of Modularity...
Image courtsy of: http://www.slideshare.net/bjhargrave/why-osgi

20. Next Level of Modularity...
● Separate class loader per module.
○ creating a class-space per module.
○ delegate class loading to other modules when necessary.
● Solves the single class path problem.
● Now you have a class loader network formed from
classloader delegation.
● This network is formed with import/export package
restrictions.
● Now we have modularity at runtime as well as compile
time.

21. Next Level of Modularity...
Classloader
Network.
Delegate each
other for
classloading
requests.
Java application. Runtime view

23. What is OSGi?
"The OSGi framework is a module system and service
platform for the Java programming language that
implements a complete and dynamic component model,
something that as of 2012 does not exist in standalone
Java/VM environments."
--Wikipedia

24. What is OSGi?
● Widely accepted specification which introduces a
standard way of building dynamic, modular systems
with Java.
● OSGi framework implementations.(Open source)
○ Eclipse Equinox.
○ Apache Felix.
○ Knopflerfish.

25. OSGi Layered Model
Image courtsy of: http://www.osgi.org/Technology/WhatIsOSGi

26. OSGi Layered Model
● Bundles
○ Bundles are the OSGi components made by the developers.
● Services
○ The services layer connects bundles in a dynamic way by offering a
publish-find-bind model for plain old Java objects.
● Life-Cycle
○ The API to install, start, stop, update, and uninstall bundles.

27. OSGi Layered Model
● Modules
○ The layer that defines how a bundle can import and export code.
● Security
○ The layer that handles the security aspects.
● Execution Environment
○ Defines what methods and classes are available in a specific platform.

28. Bundles
● Bundle is the unit of modularization in OSGi
● OSGi based application can be considered as a
collection of Bundle
● Bundles can share packages with other bundles and
hide packages from otherbundles
● How does a bundle differs from a normal jar file ?

29. Bundles...
How does a bundle differs from a normal jar file?

30. MANIFEST.MF
Bundle-ManifestVersion : 2
Bundle-Name: My First OSGi Bundle
Bundle-SymbolicName: HelloWorldBundle
Bundle-Version: 1.0.0
Export-Package: org.helloworld
Import-package: org.osgi.framework
Bundle
Exported Package
Imported Package
Private Package

31. Bundle States
Image courtsy of: http://static.springsource.org/s2-dmserver/2.0.
x/getting-started/html/ch01.html

32. Demo

33. Dynamism
Modularity achieved.. but what about dynamism?

34. Dynamism...
● The moment your instantiate a new object tight coupling
among modules occurs.
● What if I want to update the platform or part of the
platform during runtime.
● What we need is a ...

35. OSGi Services
● In-VM SOA model.
● OSGi Service registry.
● Bundles can publish/lookup services using interface
names

36. OSGi Services
public void start(BundleContext bc) {
Hashtable props = new Hashtable();
props.put("language", "en");
//Registering the HelloWorld service
bc.registerService(HelloService.class.
getName(),
new HelloServiceImpl(), props);
}

37. Acquiring Services
public void start(BundleContext bc) {
//Get the service reference for HelloService
serviceRef = bc.getServiceReference(HelloService.class.
getName());
//service reference can be null, if the service is not
registered.
if(serviceRef != null) {
helloService = (HelloService)bc.getService(serviceRef);
} else {
System.err.println("service reference not found.");
}
}

38. Listeners
● Bundle Listeners
● Service Listeners
● Service Trackers
● Declarative Services

39. Declarative Services
<?xml version="1.0" encoding="UTF-8"?>
<component name="helloservice.listen">
<implementation class="org.sample.HelloComponent"/>
<reference name="HS"
interface="org.sample.HelloService"
cardinality="0..n"
policy="dynamic"
target="(language=en)"
bind="setHelloService"
unbind="setHelloService" />
</component>

40. Demo

41. Questions

42. Thank you.