Hi Jesse,
I finally got around to doing the formal code review ( while I applied the patch ). And here are my comments:
1. Instead of overriding setApplicationContext in GetMap and Capabilities I just added a getter to AbstractService. I think this makes sense as any service will potentially need to process an extension point.
2. The extension point still needs to be the MapProducerFactory even though its a FactorySPI. This is more of miscommunication then feedback. The reason being is that the actual producer can vary based on the configuration. You hit on this with your comments in the applicationContext about the two PNG map producers, and the two SVG map producers. Look at SVGMapProducerFactory for an example.
Other then that looks great, thanks for the contribution!!
-Justin
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Justin Deoliveira
The Open Planning Project
jdeolive@anonymised.com