On Fri, Dec 30, 2011 at 6:15 AM, Stephane Bailliez <sbailliez_at_gmail.com> wrote:
>
> I'm trying to figure out if it is possible to implement a
> StringReaderProvider that delegates extraction of the generic type to other
> providers.
>
In order to do this, you would need for StringReaderProvider to be a
"component" i.e. support injection (this seems possible in jersey, see
[1]).
Then in your user-defined StringReaderProvider you should be able to
extract the type parameter and delegate extraction to the injected
StringReaderWorkers. The above seems like circular dependency
injection (where one part gets resolved with @Context and the other
part gets resolved with ServiceLoader) which I don't know how it gets
resolved in jersey but may be possible to do using setter injection
...
You actually need an extension point that is a decorator/adapter
around StringReaderWorkers (I don't think there is such an extension
point in jersey but can be emulated with param injectables).
> In some way the logic would be similar to the
> MultivaluedParameterExtractorFactory but I cannot find any way to actually
> get ahold of the list of providers (StringReaderWorkers) in such a provider.
>
> I see that everything is initialized 'manually' in WebApplicationImpl and
> the StringReaderFactory is created, configured and injected manually but I
> don't seem to find any extension point to be able to get it via normal
> injection.
>
> Any pointers ?
>
> If you wonder what this is for, this is to support Google Guava Optional<T>
> for @QueryParam. I have something that works right now, but that required me
> to define manually the list of the StringReaderProvider, as well as
> reimplemented an entire queryparam injectable provider so that is not really
> optimal while it seems everything could be done within one single
> StringReaderProvider since this is basically just a wrapper around a type.
>
I did this in samson for Form<T> and actually used user-defined
form/query param injectables as
StringReaderWorkers/MultivaluedParameterExtractorProvider decorators.
You can avoid the manual definition of StringReaderProvider since
StringReaderWorkers is an injectable interface, see [2][3][4]
regards,
George
[1] public static class RootElementProvider extends
JAXBStringReaderProviders implements StringReaderProvider
[2]
https://github.com/gsapountzis/samson
[3]
https://github.com/gsapountzis/samson/blob/master/samson-jersey/src/main/java/samson/jersey/JFormProviderInjectableProvider.java
[4]
https://github.com/gsapountzis/samson/blob/master/samson-jersey/src/main/java/samson/jersey/FormParamInjectableProvider.java