Gyrex/Concepts/Http Application Extensions

Gyrex provides a concept for defining HTTP applications. This article discusses an approach for providing extensions to those applications in a generic way.

Goals

• Allow to contribute static resources, JAX-RS resources, WebSockets, etc. to an already defined application.
• Ability to add security/authentication filters to already defined applications.
• Backwards compatibility with existing applications.

Design

• Opt-in model
  • define #initializeExtensions method in Application class which must be called by participating applications
• ApplicationExtension need to be provided as OSGi service (whiteboard pattern)
• Application scans for available ApplicationExtension services at initialization time
  • iterates over all available ApplicationExtension;
  • may have optional filter hook in Application class (isAllowedToUseExtension or so)
  • calls ApplicationExtension#activate(Application, IApplicationContext)
  • installs service listener/hook to be notified when extension goes away; calls ApplicationExtension#deactivate(Application, IApplicationContext) when unregistered
  • continues to listen for new extensions while initialized; dynamically activates and deactivates extensions as they come and go
• Security
  • Track registrations by each extensions and only allow extension to unregister aliases it registered