invoking a interface default method from within an InvocationHandler

[Jochen Theodorou]

Am 09.10.2014 19:07, schrieb Remi Forax:
> public static void main(String[] args) throws NoSuchFieldException,
> IllegalArgumentException, IllegalAccessException {
>      Lookup lookup = MethodHandles.publicLookup().in(Consumer.class);
>      Field allowedModes = Lookup.class.getDeclaredField("allowedModes");
>      allowedModes.setAccessible(true);
>      allowedModes.set(lookup, Modifier.PRIVATE);
>
>      @SuppressWarnings("unchecked")
>      Consumer<Object> consumer = (Consumer<Object>)Proxy.newProxyInstance(
>          CallingADefaultMethodInAProxy.class.getClassLoader(),
>          new Class<?>[]{Consumer.class},
>          (Object proxy, Method method, Object[] array) -> {
>              if (method.isDefault()) {
>                MethodHandle mh = lookup.unreflectSpecial(method,
> Consumer.class);
>                return
> mh.invokeWithArguments(Stream.concat(Stream.of(proxy),
> Arrays.stream(array)).toArray());
>              }
>              System.out.println("hello");
>              return null;
>          });
>
>      consumer.andThen(System.out::println).accept("default method");
>    }
>
> Not very pretty, if someone ask me I will deny to have written that code :)

lol.

The other variant is to get the Lookup constructor accepting an int, to 
make private level access possible. But is that really supposed to be a 
standard solution? I mean I could then use Unsafe too ;)

> John, I've discovered that findSpecial/unreflectSpecial doesn't honor
> setAccessible,
> given that the whole point of unreflectSpecial is to see a virtual call
> as a super call,
> it looks like a bug to me.

yes, I found the same thing strange... though given the special nature 
of invokespecial I was thinking that this limitation is there to ensure 
this "call has to be done from same class or subclass" logic. So I would 
expect for example, that if I do MethodHandles.lookup().in(Foo.class), 
while being in Foo or a subclass that it would work. But of course, that 
is of zero use if Foo is an interface and whole purpose of the exercise 
is to have a proxy that acts as that interface instead of having to 
implement the interface yourself. But I did not actually test if my 
assumption is right.

bye Jochen

-- 
Jochen "blackdrag" Theodorou - Groovy Project Tech Lead
blog: http://blackdragsview.blogspot.com/
german groovy discussion newsgroup: de.comp.lang.misc
For Groovy programming sources visit http://groovy-lang.org