Yesterday evening I did a talk about Apache Karaf and OSGi best practice together with Achim Nierbeck. Achim did the first part about OSGi basics and Apache Karaf and I did the second part about OSGi best practices.
One slide from the presentation about Karaf shows the big number of features that can be installed easily. So while the Karaf download is just about 8 MB you can install additional features transparently using maven that make it a full blown integration or enterprise application server.
OSGi best practices
In my part I showed how blueprint, OSGi Services and the config admin service can be used together to build a small example application consisting of the typical modules model, persistence and UI like shown below.
Except for the UI the example was from my first Karaf tutorial. While in the tutorial I used a simple Servlet UI that merely is able to display the Task objects I wanted to show a fancier UI for this talk. Since I met the makers of Vaadin on the last W-JAX conferences I got interested in this simple but powerful framework. So I gave it as spin. I had only about two days to prepare for the talk so I was not sure if I would be able to create a good UI with it. Fortunately it was really easy to use and it just took me about a day to learn th basics and build a full CRUD UI for my Task example complete with data binding to the persistence service.
One additional challenge was to use vaadin in OSGi. The good thing is that it is already a bundle. So a WAB (Web application bundle) deployment of my UI would have worked. I wanted it to be pure OSGi though so I searched a bit a found the vaadinbrige from Neil Bartlet. It allows to simply create a vaadin Application and factory class in a normal bundle and publish it as a service. The bridge will then pick it up and publish it to the HttpService.
The end result looks like this:
So you have a table with the current tasks (or to do items). You can add and delete tasks with the menu bar. When you select a task you can edit it in the form below. Any changes are directly sent to the service and updated in the UI.
The nice thing about vaadin is that it handles the complete client server communication and databinding for you. So this whole UI takes only about 120 lines of code. See ExampleApplication on github.
So the general idea of my part of the talk was to show how easy it is to create nice looking and architecturally sound applications using OSGi and Karaf. Many people still think OSGi will make your live harder for normal applications. I hope I could show that when using the right practices and tools OSGi can even be simpler and more fun than Servlet Container or Java EE focused development.
I plan to add a little more extensive Tutorial about using Vaadin on OSGi to my Karaf Tutorial series soon so stay tuned.
Tasklist Model and Persistence: https://github.com/cschneider/Karaf-Tutorial/tree/master/tasklist
Achim adapted another Vaadin OSGi example from Kai Tödter to Maven and Karaf: https://github.com/ANierbeck/osgi-vaadin-demo