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watak

If-Modified-Since请求的HTTP标头发出请求的条件:服务器会发送回所请求的资源,用200状态,只有当它已经给定的日期之后被最后修改。如果请求没有被修改,那么响应将是304没有任何主体的;Last-Modified头将包含最后一次修改的日期。不同于If-Unmodified-SinceIf-Modified-Since只能与GETHEAD一起使用。

与组合使用时If-None-Match,将被忽略,除非服务器不支持If-None-Match

最常见的用例是更新一个没有关联的缓存实体ETag

Header type

Request header

Forbidden header name

no

语法

If-Modified-Since: <day-name>, <day> <month> <year> <hour>:<minute>:<second> GMT

指令

<day-name> “星期一”,“星期二”,“星期三”,“星期四”,“星期五”,“星期六”或“太阳”之一(区分大小写),例: “04”或“23”

<month> “Jan”,“Feb”,“Mar”,“Apr”,“May”,“Jun”,“Jul”,“Aug”,“Sep”,“十进制“,”十一月“,”十二月“(区分大小写)

<year> 4位数年份编号,例如”1990“或”2016“。

<hour> 2位数小时编号,例如”09“或”23“分钟> 2位数分钟数,例如“04”或“59”。

<second> 2位数秒数,例如“04”或“59”。GMT

格林威治标准时间。HTTP 日期总是以 GMT 表示,从不以本地时间表示。

例子

If-Modified-Since: Wed, 21 Oct 2015 07:28:00 GMT

规范

Specification

Title

RFC 7232, section 3.3: If-Modified-Since

Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests

浏览器兼容性

Feature

Chrome

Firefox

Edge

Internet Explorer

Opera

Safari

Basic Support

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

Feature

Android

Chrome for Android

Edge mobile

Firefox for Android

IE mobile

Opera Android

iOS Safari

Basic Support

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

(Yes)

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