OSGi Introduction

Ly Minh Phuong – Social Team

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Objective

OSGi architecture overview Bundles Services Lifecycle

DemoQ&A

OSGi framework Motivation

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Why OSGi?

Java not support natively dynamic module system.(@2011)

JAR dependences management is missing.

No way to restrict using class in JAR file.

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Why OSGi?

Java not support natively dynamic module system.(@2011)

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Why OSGi?

JAR dependences management is missing.

What happened when two jar file have duplicate packages and classes ?

What happened when your classes only work with a library which version < 2.3.0 ?

Can it be prevent in run time ? No way to restrict using class in JAR file.

When writing a lib/component can we control what user can import or not ?

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Why OSGi?

Resolve in OSGi way.

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What is OSGi

OSGi alliance

Open Service Gateway initiative

Founded 1999

Specification first released in 2000

Newest version of specification is 4.3 (April 2011)

Target: embedded, desktop, enterprise application.

Widely adopted: Eclipse Equinox, Apache Felix, Glassfish, Knopflerfish, ProSyst, Hitachi SuperJ Engine, …

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Basic architect

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Bundle

Bundle

Basic deployment entity ( app, component, library)

Version convention ( major.minor.micro.qualifier )

Specify the dependence, export package, activator

Package like JAR file and added the bundle meta info

Bundle-ManifestVersion: 2Bundle-Name: Greeting ClientBundle-SymbolicName: org.foo.hello.clientBundle-Version: 1.2.1.SNAPSHOT

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Bundle Lifecycle

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Bundle dependency resolution The framework prefer already resolved bundle

If both are resolved the framework prefer highest matching version.

If the version is equal it's prefer the older one.

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Bundle Activator Bundle Activator

Define by Bundle-Activator header

Handle when bundle start/stop

public final class Activator implements BundleActivator{ public void start( BundleContext bc ) throws Exception{ .... } public void stop( BundleContext bc ) throws Exception{ .... }}

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Bundle Mainifest example

Bundle-ManifestVersion: 2Bundle-Name: Greeting ClientBundle-SymbolicName: org.foo.hello.clientBundle-Version: 1.2.1.SNAPSHOTBundle-Activator: org.foo.hello.client.Activator Import-Package: org.foo.hello;version="[1.0,2.0)"Export-Package: org.org.foo.hello.api;version="1.0"Bundle-ClassPath: .,WEB-INF/classes,WEB-INF/lib/a.jar

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Service

Service

Bundle can register/unregister service using bundle activator.

One service name can have multi provider

Service can have properties to describe the service info

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Registering a service

Programmatically using Activator

Dictionary properties = new Properties();properties.setProperty("BookStorageType", "MySQL");

bundleContext.registerService(BookStorage.class.getName(), new BookStorageImpl(), properties );

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Consuming a service

Programatically using bundleContext.getSerivce()ServiceReference bookStorageRef = bc.getServiceReference(BookStorage.class.getName());if(bookStorageRef != null){

bookStorage = (BookStorage) bc.getService(bookStorageRef);System.out.println("Got BookStorage Service");

}

Use Service ListenerActivator.javaString filter = "(" + Constants.OBJECTCLASS + "=" + BookStorage.class.getName() + ")";context.addServiceListener(new BookStorageListener(), filter);

BookStorageListener.javaclass BookStorageListener implements ServiceListener { public void serviceChanged(ServiceEvent event) { .... }}

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Service consuming

Use Service Tracker

public class XyzServiceTracker extends ServiceTracker { public XyzServiceTracker(BundleContext context) { super(context, ServiceToTrack.class.getName(), null); ... } public Object addingService(ServiceReference reference) { ... } public void removedService(ServiceReference reference, Object service) { context.ungetService(reference); ... }}

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Problems about OSGi

OSGi look great but tool and development process not widely public yet.

Not every lib is bundle.

Version management can be nightmare.

Runtime dynamic can result untested situation.

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DEMO

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Q&A