A lot of questions around the configuration of a reflective style library

[Jochen Theodorou]

On 11.07.2016 11:43, Peter Levart wrote:
[...]
> Here's a simplified idea. Suppose MyReflection uses java reflection to
> invoke target methods directly and it is already arranged so that
> MyReflection has access to hidden methods in both M1 and M2 (let's take
> the generated M1|M2Accessor(s) out of the picture for now - the idea can
> be extended to include them later). Suppose that simplified MyReflection
> is used to invoke just static methods in the module of the original caller:
>
> public class MyReflection {
>
>      public interface AccessToken {}
>
>      public static Object invoke(AccessToken accessToken,
>                                  Class<?> target, String methodName,
>                                  Class<?>[] parameterTypes, Object ... args)
>          throws IllegalAccessException,
>                 NoSuchMethodException,
>                 InvocationTargetException
>      {
>          if (accessToken.getClass().getModule() != target.getModule()) {
>              throw new IllegalAccessException("Cross module call");
>          }
>
>          return target.getDeclaredMethod(methodName, parameterTypes)
>                      // this is a reflective call, but it could as well
> be a call made by generated accessor
>                       .invoke(null, args);
>      }
> }
>
>
> The original invoker and the hidden target method in M1 could then look
> like:
>
> public class CM1 {
>
>      public static int hiddenAdd(int a, int b) {
>          return a + b;
>      }
>
>      // keep the instance of AccessToken private and only pass it to
> MyReflection
>      private static final MyReflection.AccessToken ACCESS =
>          new MyReflection.AccessToken() {};
>
>      public static void main(String[] args) throws Exception {
>          int sum = (Integer)
>              MyReflection.invoke(ACCESS,
>                                  CM1.class, "hiddenAdd", new Class<?>[]{int.class, int.class},
>                                  10, 20);
>      }
> }
>
> As long as instance(s) of AccessToken implemented by classes in M1 are
> kept private and only passed to MyReflection, MyReflection can verify
> that the one that has access to such instance is an authorized caller so
> it grants it access to hidden methods in M1.

For me you are confirming, that with MethodHandles, it will become the 
responsibility to check module access rights and that calls from hidden 
M1 to hidden M2 become possible.

bye Jochen