question: public static boolean invalidCaptcha ( final String captcha , final HttpServletRequest request ) { final HttpSession session = request . getSession ( false ) ; if ( null == session ) { return true ; } if ( Strings . isEmptyOrNull ( captcha ) || captcha . length ( ) != CAPTCHA_LENGTH ) { return true ; } final String storedCaptcha = ( String ) session . getAttribute ( CaptchaProcessor . CAPTCHA ) ; if ( null == storedCaptcha || ! storedCaptcha . equals ( captcha ) ) { return true ; } session . removeAttribute ( CaptchaProcessor . CAPTCHA ) ; return false ; }
target:  Checks whether the specified captcha is invalid.