假设我从REST Web服务获取了一个对象,并且该对象具有时间戳。此时间戳具有毫秒组件。下次我请求相同的对象我不希望它被返回,除非它已经改变,所以我使用If-Modified-Since标头。但是该标题中的日期甚至不应该有毫秒。如果我将时间戳向下舍入,我将始终将对象恢复,就像它总是被修改一样。如果我把它弄清楚,我可能会错过一些更新。在这种情况下,If-Modified-Since标题对我来说完全没用,还是我错过了什么?
答案 0 :(得分:11)
发送时间戳为毫秒的服务不符合HTTP标准。 Last-Modified
必须作为 HTTP-date 发送,§3.3.1非常明确地指定:
HTTP-date = rfc1123-date | rfc850-date | asctime-date rfc1123-date = wkday "," SP date1 SP time SP "GMT" rfc850-date = weekday "," SP date2 SP time SP "GMT" asctime-date = wkday SP date3 SP time SP 4DIGIT date1 = 2DIGIT SP month SP 4DIGIT ; day month year (e.g., 02 Jun 1982) date2 = 2DIGIT "-" month "-" 2DIGIT ; day-month-year (e.g., 02-Jun-82) date3 = month SP ( 2DIGIT | ( SP 1DIGIT )) ; month day (e.g., Jun 2) time = 2DIGIT ":" 2DIGIT ":" 2DIGIT ; 00:00:00 - 23:59:59 wkday = "Mon" | "Tue" | "Wed" | "Thu" | "Fri" | "Sat" | "Sun" weekday = "Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday" month = "Jan" | "Feb" | "Mar" | "Apr" | "May" | "Jun" | "Jul" | "Aug" | "Sep" | "Oct" | "Nov" | "Dec"
提交您正在使用的服务的错误。发送Last-Modified
或If-Modified-Since
毫秒无效。
如果亚秒级准确度很重要,则使用entity tags (ETag
)可能更合适。