Java Proxies and UndeclaredThrowableException

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Java的dynamic proxies应用广泛，尤其是在客户端/服务端架构下，客户端的调用一般都是用proxy来实现。但是，一旦proxy中的方法要抛出exception时，客户端会得到UndeclaredThrowableException，而不是真正被抛出来的exception。原因是method.invoke()只会抛出InvocationTargetException，需要手工转换成真正的exception，见下面的例子：

public class ProxyHandler implements InvocationHandler {    private InterfaceA delegate;    public ProxyHandler(InterfaceA delegate) {        this.delegate = delegate;    }    @Override        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {            System.out.println("Inside the invocation handler");            try {                return method.invoke(delegate, args);            } catch (InvocationTargetException e) {                throw e.getCause();            }        }}

参考http://amitstechblog.wordpress.com/2011/07/24/java-proxies-and-undeclaredthrowableexception/