How do I convert an existing jar file into an OSGi bundle?

Question
How do I convert an existing jar file into an OSGi bundle?

Answer, Resolution
Here's a very simple way of turning an existing jar file in an OSGi bundle, while keeping control on exported packages.

The example creates an OSGi bundle from the attached junit-4.4.jar.

Note: The method below only works in a scenario where the jar file has no dependencies on other external jar files.
Start by creating a jar's manifest file:
Manifest-Version: 1.0 

Created-By: myself 

Bundle-ManifestVersion: 2 

Bundle-Name: JUnit 4.4 bundle 

Bundle-Description: Package junit 4.4 in an OSGi bundle 

Bundle-Version: 4.4.0 Bundle-ClassPath: .,junit-4.4.jar 

Bundle-SymbolicName: org.junit.framework 

Export-Package: junit.framework,junit.extensions,org.junit.runner,org.junit,junit.textui

• Bundle-ClassPath header is set to allow embedding the original jar as is. Make sure its value matches the filename of the jar that you are going to embed in the bundle.
• Export-Package is a list of packages contained in the jar that you would like to make available to other bundles running in the OSGi Container.

Jar file
Get the jar file, in our case from http://mirrors.ibiblio.org/pub/mirrors/maven2/junit/junit/4.4/junit-4.4.jar

Create the bundle jar file by running the following command:
jar cvfm junit-4.4-bundle.jar manifest.txt junit-4.4.jar

Where manifest.txt is the name of the manifest file created above.

That's it - the resulting jar file (attached to this page as an example) is an OSGi bundle the exports the packages listed in Export-Package above, using the classes of the embedded junit-4.4.jar.