Cglib Could not support nested proxy？

[stateIs0]

Env： JDK1.8
Cglib：Spring 3.2.5

Excetption：

Exception in thread "main" org.springframework.cglib.core.CodeGenerationException: java.lang.reflect.InvocationTargetException-->null
	at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:237)
	at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:377)
	at org.springframework.cglib.proxy.Enhancer.create(Enhancer.java:285)
	at cn.think.in.java.learing.proxy.Proxy.getProxy(CglibDemo.java:50)
	at cn.think.in.java.learing.proxy.CglibDemo.main(CglibDemo.java:22)
Caused by: java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.springframework.cglib.core.ReflectUtils.defineClass(ReflectUtils.java:384)
	at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:219)
	... 4 more
Caused by: java.lang.ClassFormatError: Duplicate method name "newInstance" with signature "([Lorg.springframework.cglib.proxy.Callback;)Ljava.lang.Object;" in class file cn/think/in/java/learing/proxy/Target$$EnhancerByCGLIB$$b4f15570
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
	... 10 more

Demo:

public class CglibDemo {

    public static void main(String[] args) {
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "./");
        Target t = new Target();
        Target p = Proxy.getProxy(t);
        Target pp = Proxy.getProxy(p);
        pp.hello();

    }

}


class Target {

    void hello() {
        System.out.println("hello targe!");
    }
}

class Proxy {

    private static final Enhancer en = new Enhancer();

    static <T> T getProxy(T origin) {
        en.setSuperclass(origin.getClass());
        en.setCallback(new MethodInterceptor() {
            @Override
            public Object intercept(Object o, Method method, Object[] objects,
                MethodProxy methodProxy) throws Throwable {
                return method.invoke(origin);
            }
        });
        return (T) en.create();
    }
}

please tell me why? thank you very much.

[SylviaLee89]

I noticed that there is a similar problem at https://github.com/spring-projects/spring-framework. Perhaps we can refer to this issue to find more context about the bug (e.g. the library version since they share org.springframework.cglib libraries and caused by ClassFormatError exception?).

[fsparv]

@SylviaLee89 Not really similar. Illegal method is not the same as duplicate method. AFAICT from looking at the error/trace this issue comes up when proxying a proxy, because the proxy code adds a method named newInstance() to the proxy but it already exists if the original was already proxy.

I hit this trying to fudge around the way EasyMock handles Interfaces with default methods to solve an issue in EasierMock ( fsparv/EasierMock#2 ).

      if (interfaceWithDefaults) {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(Object.class);
        enhancer.setInterfaces(new Class[] {testObjField.getType()});
        enhancer.setCallback((MethodInterceptor) (obj, method, args, proxy) -> proxy.invokeSuper(obj,args));
        Object o1 = enhancer.create();
        type = o1.getClass();
      }
      Factory mock = (Factory) org.easymock.EasyMock.createMock(type);

[fsparv]

FWIW in my case I can get past this particular exception because Easymock shades in it's own copy of cglib, and if I depend on cglib original then the method signatures don't overlap because of differing packages for Callback. Other problems arise, but it confirms the nature of the problem.