I had looked at Spark a couple of weeks ago. I'm looking for a lightweight service-y sort of framework which just happens to have a good HTTP service available out-of-the-box. My application does back-end processing and coordinates a bunch of data feeds, thick-client HTTP requests, background processing, etc. all together. Spark was too web-centric (not a bad thing, just not what I need). OSGi was an attempt to be what I want, but its requirement of classpath isolation (a good idea conceptually) is onerous in practice. Right now, I'm using a homespun amalgam of Grizzly, Guice, and java.util.concurrent (for thread pooling), and other stuff. I really didn't want to build my own container. I'm intrigued by Apache Karaf, but OSGi is a huge pill to swallow (If you haven't debugged OSGi classloading issues, you'd be in for a treat).

In a nutshell, I want a service lifecycle container which allows me to write small, lightweight, modular services which depend on each other. The container should provide for cross-cutting concerns like monitoring, management, configuration, logging, auditability (I have concrete definitions for these things -- they're not just abstract biz-speak to me). HTTP should be an out-of-the-box, optional module. A service which exposes another service via a RESTful interface and depends upon the HTTP service should be another. For my application, services which listen to multicast data streams are just as important interfaces to the world as JSON-over-HTTP-via-REST. I want to write the HelloWorld method body and be able to do stuff like: expose it via a RESTful interface, invoke it every N seconds, inject an interface exposing the HelloWorld contract into other services, etc. When I want to know how my HelloWorld service is performing, there's a pre-built web interface which provides New Relic-esque views. I'd like to capture audit trails of the transactional flows through my services from an origination point (HTTP call, scheduled job, etc.) so I can translate failures, poor performance, usage rates, etc. into meaningful information (I wrote a poor man's version of this myself, and it's been quite useful).

Does anything like this exist? I sure can't find it. Modern JBoss (now Wildfly) might actually be closer to my requirements than I think. Perhaps I should look at the work they're doing on Version 8.