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POHow can I create a dynamic proxy in java that retains parameter annotations on methods?
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copied!<p>I currently am trying to proxy some existing JAX/RS resources, in order to allow me to use the Hibernate Validator's method validation support. However, when I proxy my class (currently using cglib 2.2), the FormParam annotation is not present on parameters in the proxy class, and so the JAX/RS runtime (apache wink) is not populating parameters. Here's some test code that shows this:</p> <pre><code>import static java.lang.annotation.ElementType.*; import static java.lang.annotation.RetentionPolicy.*; import java.lang.annotation.Annotation; import java.lang.annotation.Retention; import java.lang.annotation.Target; import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; import net.sf.cglib.proxy.Enhancer; import net.sf.cglib.proxy.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; import javassist.util.proxy.ProxyFactory; public class ProxyTester { @Target( { PARAMETER }) @Retention(RUNTIME) public static @interface TestAnnotation { } public static interface IProxyMe { void aMethod(@TestAnnotation int param); } public static class ProxyMe implements IProxyMe { public void aMethod(@TestAnnotation int param) { } } static void dumpAnnotations(String type, Object proxy, Object forObject, String forMethod) { String className = forObject.getClass().getName(); System.err.println(type + " proxy for Class: " + className); for (Method method : proxy.getClass().getMethods()) { if (method.getName().equals(forMethod)) { final int paramCount = method.getParameterTypes().length; System.err.println(" Method: " + method.getName() + " has " + paramCount + " parameters"); int i = 0; for (Annotation[] paramAnnotations : method .getParameterAnnotations()) { System.err.println(" Param " + (i++) + " has " + paramAnnotations.length + " annotations"); for (Annotation annotation : paramAnnotations) { System.err.println(" Annotation " + annotation.toString()); } } } } } static Object javassistProxy(IProxyMe in) throws Exception { ProxyFactory pf = new ProxyFactory(); pf.setSuperclass(in.getClass()); Class c = pf.createClass(); return c.newInstance(); } static Object cglibProxy(IProxyMe in) throws Exception { Object p2 = Enhancer.create(in.getClass(), in.getClass() .getInterfaces(), new MethodInterceptor() { public Object intercept(Object arg0, Method arg1, Object[] arg2, MethodProxy arg3) throws Throwable { return arg3.invokeSuper(arg0, arg2); } }); return p2; } static Object jdkProxy(final IProxyMe in) throws Exception { return java.lang.reflect.Proxy.newProxyInstance(in.getClass() .getClassLoader(), in.getClass().getInterfaces(), new InvocationHandler() { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { return method.invoke(in, args); } }); } public static void main(String[] args) throws Exception { IProxyMe proxyMe = new ProxyMe(); dumpAnnotations("no", proxyMe, proxyMe, "aMethod"); dumpAnnotations("javassist", javassistProxy(proxyMe), proxyMe, "aMethod"); dumpAnnotations("cglib", cglibProxy(proxyMe), proxyMe, "aMethod"); dumpAnnotations("jdk", jdkProxy(proxyMe), proxyMe, "aMethod"); } } </code></pre> <p>This gives me the following output:</p> <pre> no proxy for Class: ProxyTester$ProxyMe Method: aMethod has 1 parameters Param 0 has 1 annotations Annotation @ProxyTester.TestAnnotation() javassist proxy for Class: ProxyTester$ProxyMe Method: aMethod has 1 parameters Param 0 has 0 annotations cglib proxy for Class: ProxyTester$ProxyMe Method: aMethod has 1 parameters Param 0 has 0 annotations jdk proxy for Class: ProxyTester$ProxyMe Method: aMethod has 1 parameters Param 0 has 0 annotations </pre> <p>Are there any other alternatives?</p>

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