TypeLiteral injection with reflection

Question

Context : java using guice (last version)

Hi everybody, is it possible to inject some TypeLiteral with Guice by this way :

public MyClass<?,?> getMyClass(Injector injector, Class<?> a, Class<?> b)
{
     //how to Inject MyClass with type a & b ?
     //e.g : injector.getInstance(MyClass<"a class","b class">)
}

public interface MyClass<S,T>
{
     public T do(S s);
}

public class ClassOne implements MyClass<String,Integer>
{
     public Integer do(String s)
     {
          //do something
     }
}

Module :
bind.(new TypeLiteral<MyClass<String,Integer>(){}).to(ClassOne.class);
bind.(new TypeLiteral<MyClass<String,Double>(){}).to(ClassTwo.class);
...

What is the best way to handle this problem (with Guice)?

Thank you !

Answer 1

Create a ParameterizeType for your type :

// It's supposed to be internal.
// You could use sun.reflect.generics.reflectiveObjects but it is not portable.
// Or you can implement it yourself (see below)
ParameterizedType type = new com.google.inject.internal.MoreTypes.ParameterizedTypeImpl(null, MyClass.class, a, b);

Create a TypeLiteral from it:

TypeLiteral typeLiteral = TypeLiteral.get(type);

Now create injected instance:

return (MyClass<A,B>) injector.getInstance(Key.get(typeLiteral))

In practice you want to implement the ParameteriedType yourself:

 final Type[] types = {a, b};
 ParameterizedType type = ParameterizedType() {
   @Override
   public Type[] getActualTypeArguments() {
     return types;
   }

   @Override
   public Type getOwnerType() {
     return null;
   }

   @Override
   public Type getRawType() {
     return MyClass.class;
   };
}

EDIT: In fact, you can use:

Types.newParameterizedType(MyClass.class,a,b)

see Guice module with type parameters

Answer 2

In fact, I think it isn't possible. Generics are not reified at run-time. This means the information is not present at run-time. So it doesn't care what generic type you give it.

So, I think this method is not needed. Simply something like this:

public MyClass<?,?> getMyClass(Injector injector, Class<?> a, Class<?> b)
{
     return new MyClass();
     // Or maybe something like this, if you use custom constructors
     // return injector.getInstance();
}

---

Since MyClass is an interface, what you want to achieve is totally useless and impossible. How do you want to instantiate an object with a specific behavior when you only specify the param type and return type.
I think you should try to find a different way of working.