Enabling modularization through OSGi and SpringDM

Enabling Modularization through OSGi and SpringDynamicModules | by Mukul Kumar | available under EPL v1.01

Enabling Modularization through OSGi and SpringDynamicModules

Mukul KumarSystem Software EngineerIndia Software LabsIBM, [email protected]


Agenda

• OSGi as Service Platform• Spring Dynamic Modules• Summary• Q & A


OSGi as Service Platform

• Limitations with conventional Java applications• What is OSGi ?• OSGi Framework Architecture• SOA Infusion• Demo


Limitations with conventional Java applications

JAR Hell (limitations caused by JAR files)

• No Runtime boundaries between the JAR files.• Information hiding only at class level but not at modular

level.• No versioning• Classloading• Dependency on other JAR(s)


JSR 277 – Java Module System

• Module is a deployment abstraction.

• Defines a distribution format (i.e. Java Module) and a repository for collections of Java code and related resources. It also defines the discovery, loading, and integrity check mechanism at runtime.

• JSR 277 defines a static module system. There is no dynamic loading and unloading of modules/bundles, any change will require to reboot the JVM.


What is OSGi ?

• OSGi stands for Open Service Gateway Initiative.

• OSGi is Dynamic Module System for Java.

• OSGi framework implements a complete service oriented and dynamic module system.

• OSGi specification also enables modules/bundles to hide their implementation from other modules/bundles.


OSGi Framework Architecture

http://www.osgi.org


Module Layer

• Packaging: Reusable bundles contains application code and libraries.

• Code Security: Supports code hiding and explicit sharing.

• Versioning: Different versions of same JAR can be used in single VM.

• Classloading: Advance classloading schemes.

bundle bundle

bundle

bundle

bundle

bundle


Life Cycle Layer

• Offers an API for bundle life cycle management that manages modules at runtime.

• These dynamics are generally not part of applications and fully protected with security mechanism.

installed

resolved

uninstalled

active

stopping

starting

start

stop

install

uninstall

uninstall


Bundles

• A bundle mainly consists of a group of Java classes and a metadata descriptor, MANIFEST.MF file.


MANIFEST.MF


Activator

• Bundle is started by BundleActivator class.• Interface has 2 methods.

– start(): initialize and return immediately– stop(): clean up

• BundleContext gives access to framework functions.• Framework functions enables us to start/stop the group

of applications.


Service Layer

• Provides an In-VM service Model– Discover services

based on their interface or properties.

– Bind to one or more services.

OSGi Service Registry

Bundle A Bundle B

registers

get


SOA Infusion

• Based on contract (interface)

• Separate the contract form implementations.

• Dynamically discover and bind alternate implementations inside a Java VM.

• Components are reusable.

Service Contract

Componentprovides

uses

courtesy:


DEMO

• Hello OSGi• Service Registration• Service Tracker


Service Registration

• Exporting Service– MANIFEST.MF

• Export-Package: com.eclipseday.osgi.employee.service

• Importing Service– MANIFEST.MF

• Import-Package: com.eclipseday.osgi.employee.service

• This is also called Bundle Dependency Management, facilitated by OSGi Framework Module Layer.


Service Registration


Service Tracker

• Extend from class org.osgi.util.tracker.ServiceTracker


Service Tracker


Spring Dynamic Modules

• Spring Framework• What is SpringDM ?• Extender Pattern• Spring Application Context• Demo


Spring Framework

• Lightweight Container– Manages through the bean lifecycle

• Provide support for IOC– Declarative support for beans wiring

• Provide support for AOP– Advice can be applied declaratively

• Integration with Web frameworks – Spring MVC, Struts, JSF…

• Spring JDBC support and ORM integration


Without Dependency Injection


With Dependency Injection

• Based on Interface, not coupled to implementation.• Reusable• Easily testable


What is SpringDM ?

• SpringDM brings OSGi benefits in to Java EE application development.

• An OSGi Service can be imported and exported as if it were a Spring bean.

• SpringDM is also at the heart of springsource dm server.

• Download SpringDM from:http://www.springframework.org/osgi


Extender Pattern: org.springframework.osgi.bundles.extender

• Checks for the spring enabled bundles to be installed and create application/module context for those bundles.

• Spring enabled bundle:– META-INF/spring/*.xml– Spring-Context header in

MANIFEST.MF


JVM

OSGi Service Platform

Framework Bundles Application Bundles

Spring Application Contexts

SpringDM Extender Bundle Spring enabled Bundles

Spring bean

Service


Spring Application Context

• For each spring enabled bundle, Spring Application Context (or Module Context) will be created.

• Application Context will be created when bundle is started and destroyed when bundle is stopped.

• A Spring Bean can be published as if it were an OSGi Service.

• An OSGi Service can be imported as if it were a Spring Bean in that Application Context.

• Spring Beans/ OSGi Services communicate via OSGi Service Registry.

• Saves interaction with low level OSGi Framework API.


DEMO

• Exporting a Spring Bean as OSGi Service• Importing an OSGi Service as Spring Bean• Using Service/Bean


Service Export

Service Import


Using the Service


Summary

• OSGi benefits modular application development via:– Versioning– Modularity– Life Cycle Management– Service Registry

• SpringDM supports modular application development by bringing OSGi benefits and Spring IOC support together.– No need to work with low level OSGi framework API.– Manages the service dynamics internally.


Q & A


Further Queries, Feedback, Suggestions …

are welcome @

[email protected]


Thank you !

Enabling modularization through OSGi and SpringDM

Technology

service layer

service export service

summary osgi

agenda osgi

osgi specification

osgi framework module

service platform limitations

service contract component