question: @ Override public void init ( FilterConfig config ) throws ServletException { try { expiry = Math . min ( Math . max ( MIN_EXPIRY , Long . parseLong ( config . getInitParameter ( CACHE_CONTROL ) ) ) , MAX_EXPIRY ) ; } catch ( NumberFormatException nfe ) { LOGGER . warn ( "Failed to parse " + CACHE_CONTROL + " value." , nfe ) ; expiry = null ; } }
target:  Parse the Cache-Control configuration parameter as a long integer, and set the filter expiry value, modulo the minimum and maximum expiry constraints. If the configuration parameter is not present, or not a valid long integer value, then no Cache-Control headers will be applied by the filter.