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Sunday, August 27, 2017

OSGi Architecture

OSGi is a standard that defining Dynamic Component Development for Java.
Its specification that define the API to develop dynamic components in java application development. As per OSGi application composed of several components and components are packaged as bundle.

Java to build complex application is big challenge where OSGi defining way to divide application into several bundles and each bundle composed with several components.
OSGi is providing environment where all these bundles and components can communicate each other such way we can run complex application.

Component:

Component is small unit of application and it called as some feature in the application. Component cam work independently or it can collaborate with other component to full fill the requirement in the application.

Bundle:

Bundle is composed with several components and OSGi we package components as bundles and we will deploy bundles into OSGi container.

Services:

Services are part of component and it will full fill one more tasks. OSGi we can export and import services such as way we can make available services to other components or bundles.

Modules:

Module is basic terminology in OSGi modular development and these modularity concept achieved through bundles. Modules and bundles are same.

 OSGi Layers.

OSGi architecture divided into several layers. I have taken the following picture from enRoute.

Source of image: enroute

Bundles:

Bundles are packaged components developed by OSGi developers. Bundle is packaged as JAR file and we can deploy into OSGi containers.

Services:

Services layer provide mechanism to share services between bundles. It will provide environment to register services and make available to other bundles. We have concept called publish-find-bind. We have different framework to achieve this concept. Declarative Services and Apache Service Component Runtime are the implementation for this concept.

Life Cycle:

Life Cycle is responsible to manage lifecycle of bundles. OSGi bundle have several lifecycle stages install, start, update, stop and uninstall. All these stages handles in this layer.

Module:

Module layer is define the import / export the code of the bundles. Usually we will use export/import headers in the OSGi manifest file that will handle in module layer.

Execution Environment.

Execution Environment layer define the classes and methods are available to the platform.

Security:

Security layer define standards security to the OSGi applications. How your modules available to the other platforms and it will define some permission system.

Java VM

Java VM layer is provide the JAVA run time environment. Its basic layer in the OSGi.

Operating System

It will provide standard Operating System to the OSGi environments.

Deployment

OSGi provide run time container there we can deploy bundles. Bundles are standard package system where we can package all java classes and interfaces. Bundle is JAR file. We have different commands provided by OSGi command line interface to deploy bundles.

Implementation

OSGi specification implemented by several vendors’ popular vendors Equinox and Apache Felix. We can develop OSGi application which target to anyone of these implementations. Both implementations are followed the OSGi standard specification. There may be few features vendor specific but most of the implementation as per OSGi specification.

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