Re: empty interfaces via reflection

 Owen Jacobson <>
Sun, 14 Oct 2007 04:23:33 -0700
On Oct 14, 2:00 am, "Aryeh M. Friedman" <>

This is where the proxy comes in I basically wrap Proxy.invoke(....)
around all method calls and if the return type needs to be rebranded
(made by the custom classloader) it does so. This is safe because it
is conceptually illegal for a unit test to call any methods in the
returned value except to check it's values.

oops mentioned the one problem java.lang.reflect.Proxy requires all
acted on "classses" be interfaces not classes. thus the desire to
make a empty interface and wrap any rebranded class in it tempurarly
so the proxy can be used.

You will discover that creating a proxy does not expose arbitrary
random method calls, nor can the proxy be (down)cast to any interface
other than the one you specified when it was created. Java's static
type checking still applies, preventing the former, and the object the
caller invokes methods on (the proxy) doesn't have the complete
inheritance hierarchy of the proxied object. For example, the
following won't work:

public interface Proxied {}

public class Foo implements Proxied {
  public void bar () {...}

  Foo proxyForFoo = (Foo) Proxy.newProxyInstance(
    new Class[] { Proxied.class },

because the object returned from newProxyInstance is neither a Foo nor
a child of Foo.

In short, you can't get there from here; go back to working with class
loaders. I think you probably want to avoid running any user code
from the System classloader at all; if possible, you want to run each
test case inside a single classloader which can be thrown away at the
end of the run and which provides canonical definitions of each class
to the tested code.

The other traditional and, more importantly, workable tool for moving
objects' states between classloaders is serialization; obviously, this
only works if the objects in question are serializable. This is one
of the reasons EJB remote interfaces must accept only serializable
objects or primitives as arguments and only return said.

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