We wanted to add some AoP HttpClient, and had to use Java Proxy which can only proxy an interface. HttpClient 3.0 doesn't have interfaces. So here's how I got around that problem with a "retroactive interface":

1. create an interface

   public interface IHttpClient {
     int executeMethod(HttpMethod method)
       throws IOException, HttpException;
   }
   

2. extend HttpClient, and implement the interface:

   public class MyHttpClient
     extends HttpClient 
     implements IHttpClient {
   }
   

3. Use MyHttpClient as the implementation of the proxy. (I can't show the implementation of the proxy, but you should have an idea about the "retroactive interface" at this point)

Any questions?

From http://www.jroller.com/Solomon/entry/retroactive_interfaces