OSGi : Develop Simple Apps

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OSGi Activities

• Start and run the Eclipse for OSGi as installed in the previous lecture.
• Open the Subversion Perspective in Eclipse for OSGi.
• Check out the Simple Sample from OSGi Course Repository
• Run the sample and change it.
• Define the main steps involved in developing OSGi applications.
• Write a small tutorial (main steps) about using Eclipse to develop OSGi applications.

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Start the lab activities in the order defined below:

1. Check out the Service Interface
2. Check out the Service Provider
3. Check out the Service Consumer

Steps for Building Bundels

1. Study the Interfaces

• Bundle
• BundleContext
• BundleActivator

2. Define the Bundle Service Interface

2.1 Define the Java Interface that exposes the services

Let us suppose that one wants to define a service that allows the user to find a book using its isbn.

package cs.ecl.osgi.simple.bookfinder;

public interface BookFinder {
	Book findBook(int isbn) throws BookNotFoundException;
}

Define in the same bundle the classes that you need such as: Book and BookNotFoundException

package cs.ecl.osgi.simple.bookfinder;

public class Book {
	private int isbn;
	private String title;
	
	public Book(int isbn, String title) {
		super();
		this.isbn = isbn;
		this.title = title;
	}

	public String getTitle() {
		return title;
	}

	public void setTitle(String title) {
		this.title = title;
	}

	public int getIsbn() {
		return isbn;
	}

	public void setIsbn(int isbn) {
		this.isbn = isbn;
	}
}

package cs.ecl.osgi.simple.bookfinder;

public class BookNotFoundException extends Exception {
	private static final long serialVersionUID = -6184839510952070091L;

	public BookNotFoundException() {
		super();
	}

	public BookNotFoundException(String arg0) {
		super(arg0);
	}
}

2.2 Define in the MANIFEST.MF cs.ecl.osgi.simple.bookfinder

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Bookfinder
Bundle-SymbolicName: cs.ecl.osgi.simple.bookfinder
Bundle-Version: 1.0.0.qualifier
Bundle-RequiredExecutionEnvironment: JavaSE-1.6
Bundle-Vendor: Seneca College - Eclipse Course
Export-Package: cs.ecl.osgi.simple.bookfinder

3. Define the Bundle Service Provider

The service bookfinder could be used only if one implements the service. The bundle cs.ecl.osgi.simple.bookfinderservice implements BundleActivator interface in the Activator class

3.1 Define the Activator class

package cs.ecl.osgi.simple.bookfinderservice;

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

import cs.ecl.osgi.simple.bookfinder.BookFinder;
import cs.ecl.osgi.simple.bookfinderservice.internals.BookFinderImplementation;


public class Activator implements BundleActivator {

	private static BundleContext context;

	static BundleContext getContext() {
		return context;
	}
	
	public void start(BundleContext bundleContext) throws Exception {
		Activator.context = bundleContext;
		BookFinder bookService = new BookFinderImplementation();
		
		context.registerService(BookFinder.class.getName(), bookService, null);
		System.out.println(" Bookfinder service registered ");
	}
	
	public void stop(BundleContext bundleContext) throws Exception {
		Activator.context = null;
		System.out.println(" Bookfinder service stopped ");
	}
}

3.2 Define the internal implementation class BookFinderImplementation in an internal package cs.ecl.osgi.simple.bookfinderservice.internals The package will not be exposed to the outside world)

package cs.ecl.osgi.simple.bookfinderservice.internals;

import cs.ecl.osgi.simple.bookfinder.Book;
import cs.ecl.osgi.simple.bookfinder.BookFinder;
import cs.ecl.osgi.simple.bookfinder.BookNotFoundException;

public class BookFinderImplementation implements BookFinder {
	private static final Book[] BOOKS = new Book[] {
			new Book(1234, "Java Programming Language"), 
			new Book(5678, "OSGi") };

	public Book findBook(int isbn) throws BookNotFoundException {
		Book found = null;

		for (Book b : BOOKS)
			if (b.getIsbn() == isbn) {
				found = b;
				break;
			}
		if (found == null)
			throw new BookNotFoundException("No book with isbn = " + isbn);

		return found;
	}
}
//This could be any implementation: database, file system, distributed, etc.

Define in the MANIFEST.MF for cs.ecl.osgi.simple.bookfinderservice

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Bookfinderservice
Bundle-SymbolicName: cs.ecl.osgi.simple.bookfinderservice
Bundle-Version: 1.0.0.qualifier
Bundle-Activator: cs.ecl.osgi.simple.bookfinderservice.Activator
Bundle-ActivationPolicy: lazy
Bundle-RequiredExecutionEnvironment: JavaSE-1.6
Import-Package: org.osgi.framework;version="1.3.0"
Bundle-Vendor: Seneca College -  Eclipse Course
Export-Package: cs.ecl.osgi.simple.bookfinderservice
Require-Bundle: cs.ecl.osgi.simple.bookfinder;bundle-version="1.0.0"

The bundle export the package cs.ecl.osgi.simple.bookfinderservice Meanwhile, the implementation package - cs.ecl.osgi.simple.bookfinderservice.internals - is hidden to the outside world and can be change dynamically and can be changed dynamically anytime a better implementation is created.

The bundle requires the osgi framework and the interface bundle (e.g. bookfinder bundle)

Require-Bundle: cs.ecl.osgi.simple.bookfinder;bundle-version="1.0.0"

Import-Package: org.osgi.framework;version="1.3.0"

The bundle export its service (for instance, the bood finder service - cs.ecl.osgi.simple.bookfinderservice)

Export-Package: cs.ecl.osgi.simple.bookfinderservice