code: public void checkContentType(final HttpServletRequest request) {
      String reqpar = request.getParameter(getContentTypeRequestName());
  
      if (reqpar != null) {
        if (reqpar.equals("!")) {
          // Go back to unsticky content type
          setContentTypeSticky(false);
        } else {
          setContentType(reqpar);
          setContentTypeSticky(false);
        }
      }
  
      reqpar = request.getParameter(getContentTypeStickyRequestName());
      if (reqpar != null) {
        if (reqpar.equals("!")) {
          // Go back to unsticky content type
          setContentTypeSticky(false);
        } else {
          setContentType(reqpar);
          setContentTypeSticky(true);
        }
      }
    }
docs: Allow user to explicitly set the content type.
  
  @param request  Needed to locate session