Response Filter

[Brian Nice]

I have a servlet response filter that uses a wrapper class (VOStringWrapper) that extends HttpServletResponseWrapper. The response gets wrapped, then passed to the servlet, then comes back to the filter (I know this is true do to some logging I have done). In the filter I check if something was put in the session. I get the following error:
java.lang.IllegalStateException: strict servlet API: cannot call getWriter() after getOutputStream()
Here is the pertinent part of my filter code:

  
VOStringWrapper wrapper = new VOStringWrapper((HttpServletResponse)res);
chain.doFilter(req, wrapper); // goes off to servlet

HttpSession session = ((HttpServletRequest)req).getSession(true);
User user = (User)session.getAttribute(session.getId());

if (user != null) {
  if (!user.hasWorkAction("VIEW_ONLY_ACTION")) {
    req.setAttribute("Login Error", "This site is restricted to users with View-Only Access!");
    dispatchTo(req, res, "/VOError.jsp"); // method to forward to page...
  }
  else
    res.getWriter().print(wrapper.toString());
} 
else
  res.getWriter().print(wrapper.toString());

This filter works correctly under Jetty, so I am not sure that WEbLogic does not like about it. ANy help would be greatly appreciated!
Thanks
Brian