As described above, I use the following in a servlet filter before invoking the rest of the chain (e.g. chain.doFilter(req, myWrappedResp)) to retrieve values in the response.
Note: This doesn't always appear to operate as I expect. For example, I don't believe I've had setHeader() or setContentLength() called in my simple tests. It will probably make sense in the morning, but if there are any obvious flaws, I would be appreciate the pointers.
Cheers,
Erik