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.
- 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.
- Opt-in model
- define #activateExtensions method in Application class which must be called by participating applications (eg., during doInit)
- define #deactivateExtensions method in Application class which will be called automatically by Application#destroy; may also be called by Application subclasses if there lifecycle is different
- 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
- Track registrations by each extensions and only allow extension to unregister aliases it registered