php header
$testStr = "aaa";$testStr = "ccccccccc";
header("HTTP/1.1 304 Not Modified");
echo $testStr;
?>
为什么我的的代码会没有输出
回复讨论(解决方案)
你不知道304是什么意思么？
304表示正文和“上次”一样，只发header，不发正文的，通常用在响应客户端刷新的时候（就是短时间之前发送过一次了）
304可以减少服务器很多流量，但用在程序内要对“上次”判断准确，把握时间段不是容易的事
对于动态页面做缓存加速，首先要在 Response 的 HTTP Header 中增加 Last Modified 定义，其次根据 Request 中的 If Modified Since 和被请求内容的更新时间来返回 200 或者 304 。虽然在返回 304 的时候已经做了一次数据库查询，但是可以避免接下来更多的数据库查询，并且没有返回页面内容而只是一个 HTTP Header，从而大大的降低带宽的消耗，对于用户的感觉也是提高。
谢谢各位的回答，我是在做etag，都回答到点上了，问题已经解决
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