What OSGi Can Do For Me?

Two interesting usages of OSGi could be explored in my development context.

One is to use OSGi to componentize an existing complex application. Consider the OMII-UK website. As a web application, it has 3 logical functional units: the old repository that holds projects and releases and is almost obsolete, the new web front that also reads information from database about projects and releases, and the wiki based on JSPWiki. It will be nice to break them into 3 OGSi bundles to take advantage of the dynamics of OSGi bundles.

The other is to use OSGi to implement a dynamic extension framework for an originally monolithic application. In Grimoires, there is an XMLView interface that allows publishing any application domain specific service descriptions as long as they are in XML. Inside the implementation of XMLView, there is a pair of translators for each domain-specific description, translating to and from Grimoires' UDDI+WSDL+Metadata service description model. It will be good that we build XMLView over OGSi framework, and then each pair of translators will become an OSGi bundle. So if we want to support a new type of domain-specific service description, we add a corresponding bundle without bringing down Grimoires. If later this support is no longer needed, we remove the bundle without bringing down Grimoires.

These can be done because OSGi is claimed to be humble: it does not take over the whole JVM, and one Java application can even host multiple OSGi frameworks.

According to OSGi,

If you are developing software in Java then OSGi technology should be a logical next step because it solves many problems that you might not even be aware can be solved. The advantages of OSGi technology are so numerous that if you are using Java, then OSGi should be in your tool chest.

This seems reasonable because componentization looks like a natural approach towards software complexity.