proxy an interface and call a default method

[Peter Levart]

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?

Regards, Peter

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