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 Provider

2.1.1 Define the Java Interface that exposes the services

Let us suppose that you want to define a service that allows the user to find a book from the book isbn. Then the interface should look similare with this one:

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);
	}
}

Define in the MANIFEST.MF that cs.ecl.osgi.simple.bookfinder is the Exported-Package

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

2.2 Define a Concrete Bundle Provider

2.2.1 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 ");
	}
}

2.2.1 Define the internal implementation class (the class BookFinderImplementation 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 generic bundle service definition: cs.ecl.osgi.simple.bookfinder;bundle-version="1.0.0" The bundle requires the osgi framework by asking for the org.osgi.framework;version="1.3.0" package

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

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