Re: Dynamic proxy causes downstream code to not find annotations. How to solve?

Mon, 16 Mar 2015 07:44:42 -0700 (PDT)
On Monday, March 16, 2015 at 12:10:53 PM UTC, wrot=

Consider this class:
class MyClass {
    public void myMethod() { ... }
Which is coerced to this interface:
interface SomeIterface {
    public void myMethod() { ... }
If downstream code is looking for "MyAnnotation" it will not find it when=

 using a dynamic proxy.

Here is a "default" dynamic proxy, which effectively does nothing except =

to call the method and report its exceptions as normal:

   public Object invoke(Object proxy, Method method, Object[] args) throw=

s Throwable {

        try {
            return method.invoke(obj, args);
        } catch (InvocationTargetException e) {
            throw e.getCause();
The problem is that when invoke is called the Method passed to it is the =

one from the interface, not the object, so it is SomeInterface.myMethod(), =
which does not have any annotations.

What I want is to try to match the method on the actual object being prox=

ied, or perhaps some specific interface that I have identified, and effecti=
vely "lift" the actual method being invoked, to being that one.

I am running into this problem because I am using the client proxy from J=

ersey, which uses a dynamic proxy to create a REST client for me, given an =
HTTP endpoint and an interface. The problem is that when you call it, it ch=
ecks that there is a @Path annotation on the method being called, and in th=
is case that method is on a different interface, and it fails to find the a=
nnotation. So I need to make sure that I call it with the method from the c=
orrect interface.

Any suggestions? A problem you have run into before? Thanks for your thou=



Looking into this some more, I ran this code:

public class QuickTest {
    public static void main(String[] args) {
        for (Method method : Test.class.getMethods()) {

class Test implements ITest<Integer> {
    public Integer someMethod() {
        return 1;

interface ITest<T> {
    T someMethod();

And got this output:

public java.lang.Integer org.mygovscot.stars.client.Test.someMethod()
public java.lang.Object org.mygovscot.stars.client.Test.someMethod()
(... other methods on Object)

This is actually the problem in my code. The dynamic proxy gets the method =
with types erased, which corresponds to the one on the interface, so it fai=
ls to see the annotations.

I am surprised, because I thought that type erasure would mean that there w=
ould only be one method at run time, not two.

Is there some way to ensure the dynamic proxy picks up the right method?


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