proxy an interface and call a default method

[Peter Levart]

On 06/02/2016 06:34 PM, forax at univ-mlv.fr wrote:
>
>     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.

Something like the following?

http://cr.openjdk.java.net/~plevart/jdk9-dev/Proxy.invokeSuperDefaults/webrev.02/

Usage is even simpler with this API:

public class Test {

     interface I1 {
         default void m() {
             System.out.println("default I1.m() called");
         }
     }

     interface I2 {
         default void m() {
             System.out.println("default I2.m() called");
         }
     }

     interface I12 extends I1, I2 {
         @Override
         void m();
     }

     public static void main(String[] args) {

         InvocationHandler h = (proxy, method, params) -> {
             System.out.println("InvocationHandler called for: " + method);
             try {
                 return Proxy.invokeSuper(proxy, method, params);
             } catch (InvocationTargetException e) {
                 throw e.getCause();
             }
         };

         I1 i1 = (I1) Proxy.newProxyInstance(
             I1.class.getClassLoader(), new Class<?>[]{I1.class}, h);
         i1.m();

         I2 i2 = (I2) Proxy.newProxyInstance(
             I2.class.getClassLoader(), new Class<?>[]{I2.class}, h);
         i2.m();

         I12 i12 = (I12) Proxy.newProxyInstance(
             I12.class.getClassLoader(), new Class<?>[]{I12.class}, h);
         i12.m();
     }
}


Gives the following output:

InvocationHandler called for: public default void Test$I1.m()
default I1.m() called
InvocationHandler called for: public default void Test$I2.m()
default I2.m() called
InvocationHandler called for: public abstract void Test$I12.m()
Exception in thread "main" java.lang.reflect.UndeclaredThrowableException
         at $Proxy2.m(Unknown Source)
         at Test.main(Test.java:49)
Caused by: java.lang.IllegalAccessException: no such method: 
Test$I12.m()void/invokeSpecial
         at 
java.lang.invoke.MemberName.makeAccessException(java.base at 9-internal/MemberName.java:928)
         at 
java.lang.invoke.MemberName$Factory.resolveOrFail(java.base at 9-internal/MemberName.java:1064)
         at 
java.lang.invoke.MethodHandles$Lookup.resolveOrFail(java.base at 9-internal/MethodHandles.java:1692)
         at 
java.lang.invoke.MethodHandles$Lookup.findSpecial(java.base at 9-internal/MethodHandles.java:1150)
         at 
java.lang.reflect.Proxy.invokeSuper(java.base at 9-internal/Proxy.java:1151)
         at Test.lambda$main$0(Test.java:33)
         ... 2 more
Caused by: java.lang.AbstractMethodError: Test$I12.m()V
         at 
java.lang.invoke.MethodHandleNatives.resolve(java.base at 9-internal/Native 
Method)
         at 
java.lang.invoke.MemberName$Factory.resolve(java.base at 9-internal/MemberName.java:1036)
         at 
java.lang.invoke.MemberName$Factory.resolveOrFail(java.base at 9-internal/MemberName.java:1061)
         ... 6 more


...which is expected. You can't call the super abstract method. You have 
to resolve the Method object of a particular interface (I1 or I2) 
yourself in such case.

I think this is a simple API that everyone could understand.

Regards, Peter

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