problems implementing Provider<T>, where T is a generic

[Grary]

Folks,

I want to provide multiple instances of
java.util.Set<java.lang.String> in my class, but I just can't seem to
get it to work with Guice's Provider<T>.

There seems to be a hole in the documentation as far the following key
steps are concerned:

1) Can Provider<T> be implemented where T is a generic class?
2) If so, how does the binding look?

Any thoughts?

Thanks,

Grar

[Karthik Krishnan]

Have you looked at multibinding?

http://google-guice.googlecode.com/svn/trunk/latest-javadoc/com/google/inject/multibindings/Multibinder.html

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[Grary]

Karthik,

> Have you looked at multibinding?

That looks good, but a side-concern of mine is that whatever
functionality I discover in this regard also be available in Guice's
client-side cousin, GIN. For this reason, I was hoping to stick with
major releases.

Have you any thoughts on my design issue here: I'm attempting to
follow the Guice DI design imperative and not use new(), but how to
generate simple generic containers as return values? I gleaned from
Dhanji's Google IO 2009 talk that DI can help one write better code by
forcing one to think about depedencies. In this case, however, I can't
see how to get any simpler with Guice 2.0 than attempt a return of
some java.util generic container.

Thanks,

Grary

[dg]

bind( new TypeLiteral<Set<String>>(){} ).to( MyCustomStringSet.class )

Then you can

@Inject SomeClass( Set<String> strings ) { ..... }
@Inject SomeClass( Provider<Set<String>> stringProvider ) { ..... }

of course, toInstance, toProvider, work too, it's the TypeLiteral
that's the magic.

-d

[Stuart McCulloch]

2009/12/13 dg <gil...@gmail.com>

bind( new TypeLiteral<Set<String>>(){} ).to( MyCustomStringSet.class )

also from the Guice wiki:

  "Guice has complete type information for everything it injects. If you're injecting parameterized types, you can inject a TypeLiteral<T> to reflectively tell you the element type."

so you could even do this:

  bind( new TypeLiteral<Set<String>>(){} ).toProvider( MyCustomSetProvider.class );

and have TypeLiteral injected in the provider constructor, which would tell you what sort of set to provide...

--
Cheers, Stuart

[Grary]

Gents,

Thanks all -- it works. Not sure I entirely grasp the full potential
of this capability from TypeLiteral<T>, per the documentation:

"Java doesn't yet provide a way to represent generic types, so this
class does."

But, in the meanwhile, having a means to generate generic Java
containers is great.

Thanks,

Grar