Fair enough. I still think the setter and constructor is a good idea
because it is simpler then this scheme and it fits directly into IoC
containers such as spring. It can also be used in conjunction with
factory finder.
I think my initial statement was misunderstood. What i meant is there is
code that abuses the factory finder stuff. It is the difference between
using a plugin system as an extension point mechanism, and using it is a
mechanism to allow someone to plugin a particular implementation of
something. So I think code that does this:
class Foo {
FilterFactory filterFactory;
Foo() {
filterFactory = FilterFactoryFinder.findFilterFactory();
}
}
should do this.
class Foo {
FilterFactory filterFactory;
Foo( FilterFactory filterFactory ) {
this.filterFactory = filterFactory;
}
}
And for those who like using factory finder to set the library wide default:
class Foo {
FilterFactory filterFactory;
Foo () {
this( FilterFactoryFinder.findFilterFactory() );
}
Foo( FilterFactory filterFactory ) {
this.filterFactory = filterFactory;
}
}
-Justin
Martin Desruisseaux wrote:
> [EMAIL PROTECTED] a écrit :
>> I think there is a significant use case: when the user wants to set a
>> library wide default and be done with it. The alternative is to provide
>> setters for factories in every piece of code that needs them and
>> have client code inject the factories everywhere.
>> Think about people willing to use their own Feature implementation.
>> Alternative 1 is to pass a factory to every call that can build a
>> feature, altenative 2 is to set a library
>> wide chooser. Alternative 1 is not so bad, just not very convenient...
>
>
> I can elaborate on this example. Hints provides a way for users to configure
> their application in a central place, without interfering with other
> applications that use Geotools in the same JVM. A user can write the
> following
> in some central place of his code:
>
> Hints hints = new Hints(null);
> hints.put(Hints.STYLE_FACTORY, ...);
> hints.put(Hints.CRS_AUTHORITY_FACTORY, ...);
>
> Any factory not enumerated in the hints map means "any implementation is
> okay",
> so the user enumerates only the factory he care about. Note also that the
> user
> can replace
>
> hints.put(Hints.CRS_AUTHORITY_FACTORY, someFactory);
>
> by
>
> hints.put(Hints.FORCE_LONGITUDE_FIRST_AXIS_ORDER, Boolean.TRUE);
>
> which means "any factory with (longitude,latitude) axis order". It may be
> backed
> by epsg-wkt as well as epsg-hsql. I'm not aware of any way to get this
> functionality with constructor or method injection.
>
> Next, he should pass the 'hints' map either to FactoryFinder, or to the
> constructor if he wants to instantiate a Geotools object directly. Example:
>
> cof = FactoryFinder.getCoordinateOperationFactory(hints);
> or
> cof = new DefaultCoordinateOperationFactory(hints);
>
> The constructor shall uses the specified hints for obtaining any
> dependencies.
> For example:
>
> public DefaultCoordinateOperationFactory(Hints hints) {
> mtFactory = FactoryFinder.getMathTransformFactory(hints);
> }
>
> The DefaultMathTransformFactory can itself uses the hints for obtaining other
> dependencies, etc. As you can see, the hints are cascaded at construction
> time.
> So if the user creates a Hints map in some central place and pass those hints
> to
> a top-level Geotools class (for example some Canvas implementation in the
> GO-1
> module), then the hints should be cascaded to all dependencies. Passing the
> hints to every top-level Geotools class to be created (I believe there is few
> of
> them in a typical application) should cause the hints to be cascaded in every
> aspect of the application. If an other user pass a different map of hints to
> the
> same top-level Geotools classes, this different set of hints is also cascaded
> in
> new object instances without interference with the first user.
>
>
> Martin
>
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--
Justin Deoliveira
The Open Planning Project
[EMAIL PROTECTED]
-------------------------------------------------------------------------
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