Adding aspects to OSGi JAX-RS resources

Question

I'm looking for a way to add certain functionality to JAX-RS resources in an OSGI environment. Annotations seem to be a clean way to do this and I've seen it done in the Spring framework (no experience). Annotations such as @Transactional, or (what I wanted to do, requires a permission flag to be set on a user) @Permission(CREATE). However, I'm a bit stuck on how to do this in an OSGI environment.

The normal way(is it?) to go about adding aspects would be to register an aspect service that wraps the original service. If I looked it up correctly, JAX-RS resources are tracked and hooked up to an HttpService. JAX-RS resources do not implement an interface and proxies would need to be dynamically created.

How would I dynamically generate OSGI aspect services/resources that effectively hide the original resource from the JAX-RS tracker that hooks it to the HttpService? I have zero experience with existing AOP frameworks and barely any knowledge of AOP itself.

Answer 1

It is very common in the Java EE and Spring world to use interceptors and define additional behavior based on annotations. There are some solutions in OSGi as well, there is an RFP to support EJB annotations.

However, I have a different opinion. Although this looks cool, it is also magical. See the "Why not annotations, interceptors and other magic?" chapter of this README file where I wrote down my reasons. This project implements the logic that you would like to achieve with @Transactional annotation, but it only uses functional interfaces.

I think it is better to think in lambda expressions to achieve the goal you want (see the java 8 example behind the link). If it is not Java 8, you can still use anonymous classes (see jave 7 and above example behind the link). Your code will look more ugly with anonymous classes, but it will be very clear, what your code does.

Others might not like my answer. Three years ago I was one of the biggest fan of annotation scanning, weaving and interceptors. After a couple of headaches, I became an enemy of this "magical" concept.