reflection - How do I intercept a method invocation with standard java features (no AspectJ etc)?

Question

I want to intercept all method invocations to some class MyClass to be able to react on some setter-invocations.

I tried to use dynamic proxies, but as far as I know, this only works for classes implementing some interface. But MyClass does not have such an interface.

Is there any other way, besides implementing a wrapper class, that delegates all invocations to a member, which is an instance of the MyClass or besided using AOP?

Answer 1

As you note, you cannot use JDK dynamic proxies (no interface), but using Spring and CGLIB (JAR included with Spring), you can do the following:

public class Foo
{
    public void setBar()
    {
        throw new UnsupportedOperationException("should not go here");
    }

    public void redirected()
    {
        System.out.println("Yiha");
    }
}

Foo foo = new Foo();
ProxyFactory pf = new ProxyFactory(foo);

pf.addAdvice(new MethodInterceptor()
{
    public Object invoke(MethodInvocation mi) throws Throwable
    {
        if (mi.getMethod().getName().startsWith("set"))
        {
            Method redirect = mi.getThis().getClass().getMethod("redirected");
            redirect.invoke(mi.getThis());
        }
        return null;
    }
});

Foo proxy = (Foo) pf.getProxy();
proxy.setBar(); // prints "Yiha"