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vineri, 17 octombrie 2014

Modular REST applications with Karaf features for OSGi Jax-RS Connector

The purpose of this article is to let you know how easy  it is to develop modular REST (JAX-RS) applications on OSGi, particularly Apache Karaf.

For some time I'm working on improving the way I deliver applications. My focus is on quality, ease of understanding and speed of delivery. My framework of choice for some time is the OSGi platform (mostly used on top of Karaf, but I'm getting bolder - going for bare-bone, native containers). 

Regarding web applications I admit I don't like sessions and I am strongly inclined to develop stateless applications. Since I like standards and the benefits they provide, my choice for a web framework has narrowed down to JAX-RS for which there are a few implementations. 

I came across a project called osgi-jax-rs-connector who's aim is to simplify web application  development using JAX-RS on OSGi. The way it works is you write your JAX-RS annotated resources and you publish them in the registry. Once there, the JAX-RS Publisher from osgi-jax-rs-connector will find them, take notice of the annotation and publish them.  That's it.

In the project README on github, you will find links to articles detailing the whole process.

All i did was to  add a features file for Apache Karaf so you can try it out easily. I've made a pull request with my code to make it part of the original code base and hopefully it will soon. 

I'll reproduce the steps below. You start by building the project and installing the features in Apache Karaf:

    feature:repo-add mvn:com.eclipsesource.jaxrs/features/0.0.1-SNAPSHOT/xml/features
    feature:install scr http
    feature:install jax-rs-connector jax-rs-provider-moxy
    install mvn:com.eclipsesource.jaxrs/jax-rs-sample/0.0.1-SNAPSHOT
After this just go to: http://localhost:8181/sercices/greeting 

You can check the whole project on my github account in the mean time: step by step .

There are other solution out there for publishing JAX-RS resources using OSGi HttpService. Another interesting approach is Neil Bartlett's JAX-RS OSGi extender . The main advantage (in my opinion) of using the approach taken by Connector is the fact that you publish objects instead of the extender building them for you. This means that I am free to choose the way I build my object and I also have the opportunity to inject dependencies in it before I publish it  - hello CDI. I can build my objects using CDI via pax-cdi or with declarative services (as you can see in my sample code) and I am free to inject stuff in it before I expose it for registration with HttpService. That is a pretty powerful thing. I hope to show you how this is done soon. 


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