Dynamic proxy and checked exceptions

Question

How can I make my dynamic proxy throw checked exceptions?

I need a transparent wrapper for an interface which sometimes throws checked exceptions such as IOException. Is it possible without 3rd party AOP or writing my own proxy? Modifying all 20 methods of the interface by hand is not an option either.

Answer 1

What you probably are looking for is this, as Konrad mentions above:

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
        Object value = method.invoke(delegate, args);
        return value;
    }
    catch (InvocationTargetException ex) {
        throw ex.getCause();
    }
}

Source: https://web.archive.org/web/20120130204437/http://benpryor.com/blog/2006/08/15/java-dynamic-proxies-and-invocationtargetexception/

Answer 2

A dynamic proxy can throw checked exception if the exception is declared in the signature of the method of the interface it is proxying. From the Sun's Dynamic Proxy reference:

If an exception is thrown by the invoke method, it will be also thrown by the method invocation on the proxy instance.

The exception's type must be assignable to either any of the exception types declared in the signature of the interface method or to the unchecked exception types java.lang.RuntimeException or java.lang.Error.

If a checked exception is thrown by invoke that is not assignable to any of the exception types declared in the throws clause of the interface method, then an UndeclaredThrowableException will be thrown by the method invocation on the proxy instance. The UndeclaredThrowableException will be constructed with the exception that was thrown by the invoke method.