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

[José Rodolfo Freitas]

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?
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>>
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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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