Http请求头和响应头的Cache-Control如何理解

<br />Request Headersview source<br />Accept:*/*<br />Accept-Encoding:gzip, deflate, sdch<br />Accept-Language:zh-CN,zh;q=0.8<br />Cache-Control:no-cache<br />Connection:keep-alive<br />Cookie:CNZZDATA1254790698=1245005062-1429681029-%7C1429681029<br />Host:yuanzi.me<br />Pragma:no-cache<br />Referer:http://yuanzi.me/<br />User-Agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/39.0.2171.95 Safari/537.36<br /><br />Response Headersview source<br />Accept-Ranges:bytes<br />Cache-Control:max-age=259200<br />Connection:keep-alive<br />Content-Length:100922<br />Content-Type:application/javascript<br />Date:Wed, 22 Apr 2015 06:13:34 GMT<br />ETag:"55371597-18a3a"<br />Expires:Sat, 25 Apr 2015 06:13:34 GMT<br />Last-Modified:Wed, 22 Apr 2015 03:29:27 GMT<br />Server:nginx/1.6.2<br />