Overriding a method in an instantiated Java object

I would like to override a method in an object that's handed to me by a factory that I have little control over.

My specific problem is that I want to override the getInputStream and getOutputStream of a Socket object to perform wire logging.

The generic problem is as follows:

public class Foo {
    public Bar doBar() {
        // Some activity
    }
}

Where I'd like to take an instantiated Foo and replace the doBar with my own that would work as follows:

Bar doBar() {
    // My own activity
    return original.doBar();
}

For the Socket I'm going to return an InputStream and OutputStream that are wrapped by logging to intercept the data.