title: OSGI, Servlets and JPA hello world / tutorial / example
body: <p>I want to build a web application which basically is a restful web-service serving json messages. I would like it to be as simple as possible. I was thinking about using servlets (with annotations). JPA as a database layer is a must - Toplink or Hibernate. Preferably working on Tomcat. I want to have app divided into modules serving different functionality (auth service, customer service, etc..). And I would like to be able to update those modules without reinstalling whole application on the server - like eclipse plugins, user is notified (when he enters webapp's  home url) that update is available, clicks it, and app is downloading and installing updated module.</p>
  
  <p>I think this functionality can be made with OSGI, but I can't find any example code, or tutorial with simple hello world updatable servlet providing some data from database through jpa.</p>
  
  <p>I'm looking for an advice:
  - Is OSGI the right tool for this or it can be done with something simpler?
  - Where can I find some examples covering topic (or topics) which I need for this project.
  - Which OSGI implementation would be best-simplest for this task.</p>
  
  <p>*My knowledge of OSGI is basic. I know how bundles are described, I understand concept of OSGI container and what it does. I have never created any OSGI app yet.</p>