proxy an interface and call a default method

[forax at univ-mlv.fr]

----- Mail original -----

> De: "Peter Levart" <peter.levart at gmail.com>
> À: forax at univ-mlv.fr
> Cc: "Da Vinci Machine Project" <mlvm-dev at openjdk.java.net>, "jochen
> Theodorou" <blackdrag at gmx.org>
> Envoyé: Jeudi 2 Juin 2016 15:23:44
> Objet: Re: proxy an interface and call a default method

> Hi Remi, Jochen,

> On 06/02/2016 11:15 AM, forax at univ-mlv.fr wrote:

> > > > The solution could be for Proxy API to provide a MH that was already >
> > > > bound to the Proxy instance. Such pre-bound MH could not be abused
> > > > then.
> > 
> 

> > independently of any security issue, it may be a good idea but doing a
> > partial evaluation on a MH is not cheap.
> 

> I created a prototype for this:

> http://cr.openjdk.java.net/~plevart/jdk9-dev/Proxy.invokeSuperDefaults/webrev.01/

> Example usage is as follows:

> public class Test {

> interface I {
> default void m() {
> System.out.println("default I.m() called");
> }
> }

> public static void main(String[] args) {

> InvocationHandler h = (proxy, method, params) -> {
> System.out.println("InvocationHandler called for: " + method);
> MethodHandle superM = ((Proxy) proxy).findSuper(I.class, "m",
> MethodType.methodType(void.class));
> return superM.invokeWithArguments(params);
> };

> I i = (I) Proxy.newProxyInstance(
> I.class.getClassLoader(), new Class<?>[]{I.class}, h);

> i.m();
> }
> }

> It works, but in order for this to have adequate performance, caching would
> have to be added. But caching a pre-bound MH would require caching on
> per-proxy-instance basis, which would not be very efficient. So perhaps,
> instead of providing a Proxy::findSuper method that returns a pre-bound MH,
> there could simply be a method like the following in the Proxy class:

> public final Object invokeSuper(Class<?> interfaze, String methodName,
> MethodType methodType, Object ... args) { ... }

> What do you think?
yes, good idea, 
i think it should be static (and takes a Proxy as parameter) to avoid unwanted overriding. 

> Regards, Peter

Rémi 
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