OSGI Tutorial

1st July 2011 Amit Raj [email protected]

OSGI Tutorial - HelloWorld Program

Open Source Gateway Interface (OSGI) framework is meant for java programming language to build the

application in the form of several modules and to control them dynamically. It maintains the whole

lifecycle (start, stop, destroy etc) of those components. It has good integration with Spring framework

called Spring-OSGI, where you can define the OSGI services as the spring services in the context

configuration file. Eclipse, could be the best example for OSGI implementation. In 2004, Eclipse 3.0

released with the OSGI integration. In OSGI, you have to define your services and also need to take care

about the connection between those services and your application. You can install, uninstall any module

at the runtime and it allows containing more than one version of a module.

It provides two basic features – one is service platform and deployment platform. Service platform

usually allows building all your services and registering them in the registry. These services can be

accessed across the modules depending upon the source module configurations. Bundles contain the

service provider and service requesters. The deployment platform allows you to install, uninstall,

activate, deactivate, start and stop a service. These deployment functionalities can be accessed via osgi

command prompt. Each bundle usually has a manifest file which has the description of the activator of

the bundle. This activator control the starting and stopping the service.

In this tutorial, I will explain how to create the OSGI bundles and how one service defined in one bundle

can be used in other one. It includes importation and exportation of services in OSGI framework.

First of all, Open the eclipse and create a new Project by File -> New -> Project. You will get a wizard to

select the type of project.


Now select the Plug-in project and press next. Enter the project name as com.osgi.amitraj.HelloWorld

and Select the Target Platform as “an OSGI Framework - Quinox”. We will use the quinox framework for

osgi development.


Then press next button. You will get the following screen to edit some more properties if you want.


Then press next. Then you will see a screen to select the template to create an OSGI bundle. Select the

“Hello OSGI Bundle” and press finish button.


After pressing the finish button, the osgi bundle will be ready and available in project explorer. Double

click on the Manifest.mf file will look like this:


You can see this manifest file in the text format as well as shown below:


Here, I will explain some of the basic terms of this manifest file.

Bundle-ManifestVersion: It tell to use the OSGI version.

Bundle-Name: Some human readable name for the bundle.

Bundle-SymbolicName: Fully qualified name of your bundle.

Bundle-Activator: Activator class of the bundle which has the method like start and stop.

Bundle-Vendor: Human Readable vendor name.

Import-Package: The package imported by this bundle.


This is the bundle activator class which is instantiate on the OSGI framework. It contains two method

to control the life cycle. Start method is called when the bundle is started and stop method is called

when the bundle is stopped. These methods can be used in the scenarios like at the start of the

bundle, keep some open connections of a database and when the bundle stop, flush all the database

connections.

Now I will show how to run this simple example. Go to the Run and select the Run configurations.

Run-> Run Configurations. Double click on OSGI Framework will create a new OSGI Framework Run

Configuration. Then select your bundle in workspace and org.eclipse.osgi in the Target Platform like

below:


Then press Apply and Run button. It will start the osgi console and you can see the bundle starting

message as shown in the below snapshot.


And your first OSGI application is ready.

This was very easy but the complications starts when you have many bundles and you want to access

other bundle’s services. In that case, you have to import the services from other bundles.

OSGI Tutorial

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