2 Replies Latest reply on Feb 8, 2010 6:38 PM by Roman Borschel

    Scope-widening injection

    Roman Borschel Newbie

      Hi,


      from my previous experience with injectors, mainly Guice, I am aware of the scope-widening injection problem and I've been trying to find out how Weld behaves in this regard, especially since I saw the example from chapter 3 of the reference documentation where a @RequestScoped bean (Credentials) is injected into a @SessionScoped bean (Login).


      With Guice this is considered a bad thing since the bean in the narrower scope effectively continues to live on with the wider scoped bean it is injected into:



      It is usually an error for a @Singleton or @SessionScoped object to depend on an @RequestScoped one. Should you require an object in a narrower scope, inject a Provider of that object.

      (http://code.google.com/p/google-guice/wiki/Scopes)


      I experimented with the example from chapter 3 of the documentation by injecting the Credentials bean in the constructor of the Login bean (without providing a separate setter). Even in this case, Weld apparently replaced/reinjected a new Credentials instance upon subsequent invocations of login() in different requests. I assume this might be expected even though I currently have a bad feeling about this as such behavior is not reproducable outside of the container/weld, i.e. in a unit test, without resorting to reflection. When used programmatically there can obviously only be 1 Credentials instance associated with a Login instance if it is injected in the constructor and there is no setter.


      Even though Weld (re)injects the Credentials instance on subsequent requests (probably through reflection), I still think the last injected instance is subject to the scope-widening problem since it will live on together with the session-scoped Login instance.


      So my questions are:


      1) Is this current behavior of Weld correct?
      2) Is this behavior described in the spec?
      3) Anyone else care to share his thoughts on the scope-widening injection problem with regard to Weld?


      Thanks!


      Roman