Specifying generic collection type param at runtime (Java Reflection)

Question

I\'d like to get the generic type of a collection, using reflection, at runtime.

Code (JAVA):

Field collectionObject = object.getClass().getDeclaredF         


        

Answer 1

You can absolutely do what you want. Type erasure means you can't inspect an instance of a collection for its generic type, but you can certainly inspect a field for its generic type.

class Thing {
  List foo;
}


Field f = Thing.class.getDeclaredField("foo");
if( Collection.class.isAssignableFrom( f.getType() ) {
   Type t = f.getGenericType();
   if( t instanceof ParameterizedType ) {
     Class genericType = (Class)((ParameterizedType)t).getActualTypeArguments()[0];
     if( Persistable.class.isAssignableFrom( genericType ) )
         return true;
   }
}

There's a lot of things which can go wrong here, for example, if you have

Class Thing {
  List foo;
}

then the above won't work.