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Monday, August 21, 2017

OSGi Sample Bundle Development with Eclipse

OSGi is java modularity development framework. We can divide complex application into multiple modules and OSGi will responsible to communicate all modules and make it as single application.

OSGi is framework provides the run time environment so that all these module can communicate each other. In OSGi terminology we can call each unit as bundle. Bundle is independent component in OSGi and it can run in OSGi container. OSGi container is responsible to handle lifecycle of bundle.

Follow below articles for Basics of OSGi and Bundles





In this article we are going to see develop basic bundle development using eclipse and will run in OSGi run time environment.

Basic OSGi bundle development without eclipse and run in Apache Felix OSGi run time environment was explained in below article.


Prerequisite.

Install Java 8 and set JAVA_HOME environment variable.

Download latest version of Eclipse from below link


We are using eclipse-jee-oxygen for this example.

Any bundle in OSGi need activator java class and it is responsible for managing bundle lifecycle in the OSGi container. So each activator class should extends “BundleActivator”.
When we create bundle with eclipse it will create basic template with Activator class and if we observed the activator class, that extends “BundleActivator” class.

Once you download the eclipse extract it local machine then you can find “eclipse” directory. Navigate to “eclipse” then click on eclipse icon then eclipse will be started and initially it will ask workspace for your projects then select your workspace directory.



Create OSGi sample bundle in Eclipse.

Go to File à New à Project

It will open project selection Dialog then select “Plugin-in Project” click on next.



Once click on next then you can see another dialog there we need to provide your project name then click on next.

Project Name: com.liferaysavvy.example.LiferaySavvyWorld
Plugin-in Targeted Run with Select OSGi framework à Standard



Once click on next we can see other dialog there it will ask information which will be used in the bundle MANIFEST file. Information like name, version, vendor and execution environment.

Click on Generate Activator class check box then give your Activator class name.


Once click on Next it will ask you select OSGi template and click on Crete Plugin using template then select “Hello OSGi” so that it will generate bundle with activator class with lifecycle methods



 Finally click on finish button then bundle will create with basic activator class.
The following is basic OSGi bundle project view in eclipse



Activator

Activator is java class which handle the bundle lifecycle management in the OSGi container. It will extends the “BundleActivator” class. We have different lifecycle methods as follows

start(--) :  This method will take the argument BundleContext and container will invoke this method to start bundle.

stop(--): This method also take BundleContext as argument and OSGi container will invoke this method to stop bundle.


package com.liferaysavvy.example.liferaysavvyworld;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;

public class Activator implements BundleActivator {

     /*
      * (non-Javadoc)
      * @see org.osgi.framework.BundleActivator#start(org.osgi.framework.BundleContext)
      */
     public void start(BundleContext context) throws Exception {
           System.out.println("Say Liferay Savvy World!!");
     }
    
     /*
      * (non-Javadoc)
      * @see org.osgi.framework.BundleActivator#stop(org.osgi.framework.BundleContext)
      */
     public void stop(BundleContext context) throws Exception {
           System.out.println("Goodbye Liferay Savvy World!!");
     }

}


MANIFEST.MF:

MANIFEST.MF is deployment descriptor for the bundle and have more information and it will be used by OSGi container. This is core resource of the bundle.


Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: LiferaySavvyWorld
Bundle-SymbolicName: com.liferaysavvy.example.LiferaySavvyWorld
Bundle-Version: 1.0.0.qualifier
Bundle-Activator: com.liferaysavvy.example.liferaysavvyworld.Activator
Bundle-Vendor: LIFERAYSAVVY
Bundle-RequiredExecutionEnvironment: JavaSE-1.8
Import-Package: org.osgi.framework;version="1.3.0"


Bundle-ManifestVersion:

 This header tells that bundle follows the OSGi specification and value 2 specified, it is following SGi specification Release 4; if it is value 1 its means it is following the compliant with Release 3 or earlier.

Bundle-Name

Its human readable bundle name

Bundle-SymbolicName:

Its important header for bundle and it is unique name used to refereeing it in other bundles when it communicate to other bundles.

Bundle-Version:

Its simple version number for the bundle. We can start and run version specific bundles in the OSGi container.

Bundle-Activator

Bundle-Activator headers tells the Activator class name and it will used to manage life cycle of bundle by OSGi container.

Bundle-Vendor

The Bundle-Vendor header is just human readable name which tell the vendor who implemented the bundle.

Bundle-RequiredExecutionEnvironment:

Which tell the Jave environment is required to execute the bundle.

Import-Package

This header is very important and it tells which packages are required to execute the bundle. When the bundle depends on the other bundle then we have specify the bundle symbolic name so that it will be handled by the OSGi container. Basically each bundle must import OSGi implantation bundle it’s like “org.osgi.framework;”

Executing a bundle

Select bundle and right click on bundle

Run As à Run Configuration





Select your bundle and Select “org.eclipse.osgi” for Target platform then Apply à Run



You can see Output in the console as follows. Bundle will be started by OSGi container then it will invoke activator start method start() then we can see message in the console.





If you want execute bundle in Apache Felix environment then select Apache Felix OSGi implementation for Targeted platform.
Just type Felix in the filter text input then you can see Felix implementation jars.



If you want execute bundle in OSGi equinox then select targeted platform equinox

We can also export bundle and execute in standalone OSGi containers. Just export bundle as JAR file from eclipse and run jar file in other OSGi containers
Here is example how to run bundle in Apache Felix Environment. Look at “Install and Start bundle in OSGi” Section.


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