Gabriel Roldán a écrit :
> PropertyAccessorFactory.createPropertyAccessor(...) receives a Hints.
> It is only called by PropertyAccessors.findPropertyAccessor, which should
> pass
> the Hints to PropertyAccessorFactory.createPropertyAccessor.
> In turn, PropertyAccessors.findPropertyAccessor gets called by
> AttributeExpressionImpl.evaluate(Object), but allways passes null in place of
> Hints.
> So the question is, how do I actually pass some hints to
> PropertyAccessors.findPropertyAccessor ?
My intend with org.geotools.factory was to handle this kind of case as below:
1) Hints are given to AttributeExpressionImpl constructor.
2) AttributeExpressionImpl constructor uses the hints in order to resolve the
factory dependencies right away, and keep the reference to Factory objects
in its private fields.
3) AttributeExpressionImpl constructor declares the dependencies resolved
at (2) in its "implementation hints" field, if any.
I believe that this is the same idea than constructor injection, except that
dependencies are passed as hints rather than explicit constructor arguments and
step 3 doesn't exist for constructor injection.
> If it is just an unfinished edge of the thing, I wonder if the following
> would
> be correct:
> - Add a constructor to AttributeExpressionImpl that receives a Hints.
> - Make FilterFactoryImpl pass the Hints it receives in its constructor to the
> AttributeExpressionImpl it creates.
Yes, this is the same idea than what I wrote above, except that I would suggest
to resolve the hints right at AttributeExpressionImpl construction time if
possible, both for performance reason and making the system more predictable.
> I guess I'm making something very wrong, as the above approach wouldn't work
> neither, as I can't pass a hints with, say, an instance of NameSpaceSupport
> as value, because FactoryRegistry will check that for equality against what
> FilterFactory.getImplementationHints() returned. So it seems there's no way
> of passing a "context" to the filter factory, neither to the
> AttributeExpressions, in order to be able of making them namespace aware.
Unless there is some bug, FactoryRegistry checks for equality against
FilterFactory.getImplementationHints() only in order to see if an existing
instance matches the requested NameSpaceSupport. If no one are found, it should
creates a new factory with the given NameSpaceSupport.
> and afaik, at the geotools level we arent applying dependency injection for
> this kind of stuff neither...
Hints are basically constructor injections with dependencies specified in a
HashMap rather than explicit argument constructors. Dependencies in HashMap
provide more flexibility at the expense of less readability, but both systems
could live together. If something can't be done with hints, it is likely that
this particular piece of code is not designed in a way that looks like
constructor injection.
Martin
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