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文字

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

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Chrome

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(Yes)

Feature

Android

Chrome for Android

Edge mobile

Firefox for Android

IE mobile

Opera Android

iOS Safari

Basic Support

(Yes)

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(Yes)

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