On Mon, 2006-03-06 at 07:11, Anil Gangolli wrote:
> Allen Gilliland wrote:
>
> > I believe the relevant example is a case where someone looks up a bean
> > > directly rather than working through an interface or other class. In
> > > our current implementation we expect that everyone uses
> > > Roller.getXXXManager() to get access to a manager class by working
> > > through an interface. Using Spring someone could bypass using the
> > > Roller interface by simply calling ctx.getBean("userManager").
> > >
> > > Again, I'm not sure if this is really a problem, but it seems reasonably
> > > important to me.
> Normally, following the dependency injection pattern, a bean would have
> a private field with the interface type (e.g. UserManager) and a setter
> setUserManager(UserManager userManager) that would get called at
> initialization by the BeanFactory. Properly written, the bean never
> knows the implementation type. It also doesn't know how to find an
> instance. It just has it set by some outside entity, which is generally
> the BeanFactory but could be something else that instantiates and
> configures it.
>
> Any use of ctx.getBean("userManager") is a deviation from the
> dependency injection pattern back to the "service locator" pattern. It
> breaks the pattern in two ways. It uses an explicit service lookup and
> it makes the bean context-aware. Hence it would always be a bit suspect
> and one should have to justify any such pattern deviations with
> legitimate reasons (which there may be cases). Any occurrences should
> raise eyebrows, concerns, and requests to rewrite the offending code in
> the same way as seeing, say, new HibernateUserManagerImpl(...) (aack!)
> in someone's code today --okay maybe not that strong of a no-no, but
> leaning in that same direction.
I think we are saying the same thing here. Basically, you are suggesting that
we monitor code as it goes into the repository and make sure nobody makes
inappropriate calls to ctx.getBean("userManager") in places where they aren't
supposed to, right?
I am still interested in seeing a full proposal, but my next question is what
is to become of the Roller interface? Right now most of the
Roller.getXXXManager() methods just return the proper implementation of each
Manager class. With Spring would we replace the bodies of those methods with
ctx.getBean("XXXManager")? If so then does the Roller interface really serve a
purpose moving forward?
-- Allen
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