What is the use of converting jars to bundles in WAB(OSGI)?

Question

After exploring the OSGi framework, I had developed a sample web application.The Web Application Bundle(.war or .jar) is packaged inside an eba. The war file contains a bunch of embedded jar files in its WEB-INF/lib directory.These jars have been converted to OSGi bundles(using maven-bundle-plugin) with the required export and import packages as per the relation between the jars. Now I have to even mention all these jars(WEB-INF/lib) in the bundle-classpath. The above works because a bundle(wab is also a bundle) can include one or more jarfiles within it, and use a Bundle-Classpath manifest.mf entry to point to them.

Incase I dont include the jars in the bundle-classpath I get a ClassNotFoundException.

The question is,then there's no point converting the jars to osgi bundles.Obviously all the jars in the WEB-INF/lib are loaded by the same class loader(i.e wab's class loader) ,so then we are not reaping the major benefits of OSGi which is mainly a per bundle classloader concept?

Answer 1

Putting jars inside the WEB-INF/lib is the old-style normal-java way of handling dependencies, and putting them outside the war is the new-style OSGi way of handling them.

By packaging your war's dependencies in WEB-INF/lib, you're treating them as normal jars (remember a bundle is also a jar). So in that case, you're right that there wasn't much point in using bundles.

One of the benefits of using wabs instead of wars is to get away from the dreaded 100 Mb monolithic war. Rather than packaging the bundles inside WEB-INF/lib, try having the war import the packages it needs using Import-Package:, and package the dependencies inside the eba. (If you don't remember to have the war import the packages it needs, you'll get the class not found exceptions you were seeing, because the OSGi container won't know your war needs those packages.)