OSGiThe Dynamic Module System for JavaTM

OS

GiMotivation Growing complexity requires not only highly modular

code, but also systems that are dynamically extensible

Because there should be simpler way to construct software systems than writing , writing, and writing …

No matter which problem domain is your area of concern◦ Embedded systems need to adapt to changing requirements

even though they are deployed out in the field◦ Server applications must be configurable and manageable

without down time◦ Client applications must respond to user desires for new

functionality instantaneously

OS

GiProblems to AddersLack of PortabilityStale DevicesSoftware SizeSoftware ComplexityLimits OO TechnologyQuality of Service

OS

GiBackgroundStarted as an embedded platform for the

“home gateway”

Originally under the JCP as JSR-8 (1999)

Maintained by OSGi alliance, consists of a large number of big companies.

Current version: OSGi Release 4.2 (JSR-294)

OS

GiIntroductionAn interesting platform for creating dynamically

extensible applications

Provides a service-oriented, component based environment

Offers standardized ways to manage the software lifecycle.

OSGi technology is Universal Middleware.

OS

GiWhat we can achieve Resolves many deficiencies associated with

conventional approaches for modularity and dynamism◦ Provide a module concept

Explicit sharing of code (i.e., importing and exporting)

◦ Automatic management of code dependencies Enforces sophisticated consistency rules for class

loading

◦ Life-cycle management Manages dynamic deployment and configuration

OS

GiArchitectural Overview

OS

GiFramework Layers

L3 - publish/find/bind service model to decouple bundles

L2 - independent life-cycle of bundles without JVM restarts

L1 - a module (or bundle) uses classes from other bundles in a controlled way

L0 - well defined profiles that define the environment in which bundles can work

OS

GiModule Layer Unit of deployment is bundle, a JAR Separate class loader per bundle Multi-version support (side-by-side) Explicit code boundaries and

dependencies Metadata in the manifest Automatic wiring based on version

ranges

OS

GiLife-cycle Layer

Managed life cycle◦ States for each bundle;

Allows updates of existing bundles.◦ Dynamically install, start,

update, and uninstall

OS

GiService Layer Service interfaces allow bundles to

interact by binding interfaces, not implementations

Publish/find/bind intra-VM service model

OS

GiDynamic Service Lookup

OSGi Framework

Provided Service

Provided Package

installbundle.jar

Automatic package dependency resolution

Manual service dependency resolution Existin

g Bundle

Installed

Bundle

Resolv-ed Bundle

resolve bundle

OS

GiOSGi Service AdvantagesLightweight services

◦ Direct method invocation

Good design practice◦ Separates interface from implementation◦ Enables reuse, substitutability, loose coupling, and late binding

Dynamic◦ Loose coupling and late binding make it possible to support

run-time dynamism

Application's configuration is simply the set of deployed bundles◦ Deploy only the bundles that you need

OS

GiPaint ProgramCreate a simple Swing-based paint programDefine a SimpleShape interface to draw shapes

◦ Different implementations of SimpleShape can be created to draw different shapes

◦ Each shape has name and icon properties◦ Available shapes are displayed in tool bar

To draw a shape, click on its button and then click in the drawing canvas◦ Shapes can be dragged, but not resized

Support dynamic deployment of shapes

OS

GiHigh Level Architecture

Best practice – Try to

centralize interactionwith OSGi API so that

other componentsremain POJOs...onlyShape Tracker willinteract with OSGi

API.Best practice – Do

notmake assumptions

about threads...since we

are creating a Swingapplication, Shape

Tracker sends events on

Swing thread.

Main applicationwindow – gets dynamically

injectedwith available

shapesfrom the Shape

Tracker..

Actual shapeimplementation.

Injected “proxied” shapeimplementation to hideaspects of dynamismand provide a defaultimplementation.

Component that draws the

shape in parent frame; looks

up shape via Drawing Frame

rather than having a direct

reference..

OS

Gi

DEMO

OS

GiAdoptionApplications can leverage OSGi

functionality in two ways◦Bundled application

Build entire application as a set of bundles that will run on top of a framework instance

◦Hosted framework Host a framework instance inside the

application and externally interact with bundles/services

OS

GiAdoption (Bundled vs Hosted)Building your application as a set of bundles is

the preferred approach◦ Allows all parts of application to benefit from OSGi

modularity and dynamism◦ Allows application to run on any framework◦ However, it is not always possible to bundle

application, e.g., legacy situationsHosted framework approach allows piecemeal

OSGi adoption◦ Will likely tie application to a framework

implementation