Preface

I first used Java EE many years ago, in 2002. (Yes, Stateless Session Beans and Passivated Entity Beans, stop hiding at the back—I’m talking to you.) I can’t remember when I started using OSGi, but it was also a long time ago. Nonetheless, until recently, I’d never used the two technologies at the same time. If I was writing a desktop application or an application server (as one does), I used OSGi. If I was writing a web application, I used Java EE.

But OSGi seemed the most natural way to develop a working system. When I was writing Java EE applications, the thought of leaving my dependencies to chance or exposing all the internals of my JARs made me pretty uneasy. It felt downright icky. What if classes I needed weren’t on the classpath when my application was deployed? What if the classes I needed were there, but the version was incompatible with the one I used when I was developing? What if a colleague coded against one of my internal classes, and then I refactored and deleted it? What if I accidentally coded against the internals of a library I was using? And wasn’t there a cleaner way to get hold of interface implementations than the reflective factory pattern? Applications might work in the short term, but it felt like an accident waiting to happen.