Boolean isResponseCorrect =Boolean.FALSE;
           //remenber that we need an id to validate!
           String captchaId = httpServletRequest.getSession().getId();
           //retrieve the response
           String response = httpServletRequest.getParameter("j_captcha_response");
           // Call the Service method
            try {
                isResponseCorrect = CaptchaServiceSingleton.getInstance().validateResponseForID(captchaId,
                        response);
            } catch (CaptchaServiceException e) {
                 //should not happen, may be thrown if the id is not valid
            }

//do something according to the result!