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

[Ales Justin]

To reply, what we already discussed on irc.

This will do it:

         Class<RequestHandler> clazz = (Class<RequestHandler>) tmp;

         InjectionTarget<RequestHandler> it = manager.createInjectionTarget(manager.createAnnotatedType(clazz));
         CreationalContext<RequestHandler> cc = manager.createCreationalContext(null);
         // handler = it.produce(cc); // no need for this, if you already have an instance
         it.inject(handler, cc);


https://github.com/capedwarf/capedwarf-green/blob/master/server-api/src/main/java/org/jboss/capedwarf/server/api/servlet/WeldServlet.java

On Dec 7, 2011, at 1:21 PM, José Rodolfo Freitas wrote:

> Ales and All,
> 
> when
> 
>  @Inject
>  GenericQuery<String> gqs;
> 
> my producer do:
> 
>  new GenericQuery(clazz)
> 
> And then @Inject inside GenericQuery does not work (since I'm using new).
> 
> What's the best approach in this situation?
> 
> Using BeanManagerProvider.getInstance() inside GenericQuery constructor to provide instances for the objects I want to inject?
> 
> 
> On Tue, Dec 6, 2011 at 9:29 PM, José Rodolfo Freitas <joserodolfo.freitas at gmail.com> wrote:
> that´s an awesome solution Ales!
> I didn´t thought that I could obtain the parametizedType that way!
> Testing this will be my first task tomorrow morning.
> 
> thank you all for your ideas.
> 
> 
> On Tue, Dec 6, 2011 at 8:55 PM, Jason Porter <lightguard.jp at gmail.com> wrote:
> 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
> 
> 
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> 
> 
> 
> -- 
> 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
> 
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