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Dynamic method invocation on Proxy object?

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  Dynamic method invocation on Proxy object? Sebastian <sebastian@undisclosed.invalid> - 2012-02-08 09:19 +0100
    Re: Dynamic method invocation on Proxy object? Steven Simpson <ss@domain.invalid> - 2012-02-08 10:34 +0000
      Re: Dynamic method invocation on Proxy object? Sebastian <sebastian@undisclosed.invalid> - 2012-02-08 15:16 +0100

#11845 — Dynamic method invocation on Proxy object?

How can I dynamically invoke a method on a Proxy, where the method 
belongs to one of the proxied interfaces?

Normally (i. e. in the non-proxy case), one would do something like this:

protected Object invokeDelegated( Method m, Object[] args,
                                   Object delegate ) throws Exception
{
   // m is a method from an interface that is not implemented by delegate
   // find the corresponding method in delegate interface and invoke
   Class<?>[] parameterTypes = new Class[args.length];
   for( int i = 0; i < args.length; i++ ) {
     parameterTypes[i] = args[i].getClass();
   }
   Method meth = delegate.getClass().getMethod( m.getName(),
                                                parameterTypes );
   return meth.invoke( delegate, args );
}

However, when delegate is itself a proxy, then delegate.getClass() will 
give me Proxy, which is not what I'm looking for. How can I dynamically 
invoke the methods in the proxied interfaces?

-- Sebastian

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#11850

On 08/02/12 08:19, Sebastian wrote:
> However, when delegate is itself a proxy, then delegate.getClass() 
> will give me Proxy,

Are you sure?  I get $Proxy0 from this:

import java.lang.reflect.*;

public class GetProxyClass {
     public static void main(String[] args) throws Exception {
         ClassLoader classLoader =
             ClassLoader.getSystemClassLoader();
         InvocationHandler behaviour = new InvocationHandler() {
                 public Object invoke(Object proxy, Method method,
                                      Object[] args) {
                     System.out.println("Called " + method);
                     return null;
                 }
             };
         Object proxy =
             Proxy.newProxyInstance(classLoader,
                                    new Class<?>[] { Runnable.class },
                                    behaviour);
         Class<?>  proxyClass = proxy.getClass();
         System.out.println("Proxy class is: " + proxyClass);

         Method m = proxyClass.getMethod("run", new Class<?>[0]);
         ((Runnable) proxy).run();
         m.invoke(proxy);
     }
}

Output:

Proxy class is: class $Proxy0
Called public abstract void java.lang.Runnable.run()
Called public abstract void java.lang.Runnable.run()

It also demonstrates a method on the implemented interface being looked 
up and invoked.

-- 
ss at comp dot lancs dot ac dot uk

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#11852

Am 08.02.2012 11:34, schrieb Steven Simpson:
> On 08/02/12 08:19, Sebastian wrote:
>> However, when delegate is itself a proxy, then delegate.getClass()
>> will give me Proxy,
>
> Are you sure? I get $Proxy0 from this:
>
[coding snipped]
>
> Output:
>
> Proxy class is: class $Proxy0
> Called public abstract void java.lang.Runnable.run()
> Called public abstract void java.lang.Runnable.run()
>
> It also demonstrates a method on the implemented interface being looked
> up and invoked.

Thanks for that. I found my mistake - the reason that I could not find 
the target method turned out to be different classloaders for the 
argument types, so the signatures did not match.

-- Sebastian

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