[seam-dev] CDI with generic class and the hell of type erasure.

[Jason Porter]

Nice solution Ales, wish I'd thought of it :)

On Tue, Dec 6, 2011 at 15:45, Ales Justin <ales.justin at gmail.com> wrote:

> You could do something like this:
>
>     @SuppressWarnings({"unchecked"})
>     @Produces
>     public GenericQuery injectClass(InjectionPoint ip) {
>         Annotated annotated = ip.getAnnotated();
>         Class clazz = Object.class;
>         Type type = annotated.getBaseType();
>         if (type instanceof ParameterizedType) {
>             ParameterizedType pt = (ParameterizedType) type;
>             clazz = (Class) pt.getActualTypeArguments()[0];
>         }
>         return new GenericQuery(clazz);
>     }
>
> --
>
>     @Inject
>     GenericQuery<String> gqs;
>     @Inject
>     GenericQuery<Number> gqn;
>
> --
>
>         System.out.println("GQS: " + gqs.getClazz());
>         System.out.println("GQN: " + gqn.getClazz());
>
> --
>
> GQS: class java.lang.String
> GQN: class java.lang.Number
>
> --
>
>
> https://github.com/alesj/cdi-arq-workshop/commit/64860f15197be40a7714dfd8a7da931c1db11411
>
> HTH
>
> -Ales
>
> Hey guys, how you doing?
>
> I'm trying to achieve something that might be impossible, but before
> concluding that, I'd like to ask you, CDI gurus!
>
> I have the following class:
>
> public class Foo<T> {
>
>     public TypedQuery<T> getQuery(){
>
>     }
>
> }
>
> As you can Imagine, inside my getQuery method, I'd have to use "T.class"
> to make it TypedQuery. which is impossible due java generics type erasure.
>
> so I'd have to build a private field to hold the t.class for me.
>
> public class Foo<T> {
>
>     private Class<T> klass;
>
>      public TypedQuery<T> getQuery(){
>
>     }
>
>     public void setKlass(Class<T> klass){
>         this.klass = klass;
>     }
> }
>
> The problem is that forcing this 'setKlass' feels very ugly to the api,
> and it's not very error prone, since one could easily forget to set this
> configuration.
>
> So I had an Idea: force the setKlass inside the constructor:
>
> public class Foo<T> {
>
>     private Class<T> klass;
>
>     public Foo(Class<T> klass){
>         this.klass = klass;
>     }
>
>     public TypedQuery<T> getQuery(){
>
>     }
>
> }
>
> Unfortunatelly, this breaks cdi, since it cannot inject it anymore. At
> least AFAIK.
>
> So, is there a way out of this? maybe using a secret solder feature?
> _______________________________________________
> seam-dev mailing list
> seam-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/seam-dev
>
>
>
> _______________________________________________
> seam-dev mailing list
> seam-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/seam-dev
>
>


-- 
Jason Porter
http://lightguard-jp.blogspot.com
http://twitter.com/lightguardjp

Software Engineer
Open Source Advocate
Author of Seam Catch - Next Generation Java Exception Handling

PGP key id: 926CCFF5
PGP key available at: keyserver.net, pgp.mit.edu
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.jboss.org/pipermail/seam-dev/attachments/20111206/9438cbe2/attachment.html