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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

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