至于文档https://docs.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html
大写字母
D代表a中的天数
year，如果您想要a中的天数，
month则应使用小写
d。
同为
YYYY和
yyyy：
Letter Date or Time Component Presentation ExamplesG Era designator Text ADy Year Year 1996; 96Y Week year Year 2009; 09M Month in year Month July; Jul; 07w Week in year Number 27W Week in month Number 2D Day in year Number 189d Day in month Number 10F Day of week in month Number 2E Day name in week Text Tuesday; Tueu Day number of week (1 = Monday, ..., 7 = Sunday) Number 1a Am/pm marker Text PMH Hour in day (0-23) Number 0k Hour in day (1-24) Number 24K Hour in am/pm (0-11) Number 0h Hour in am/pm (1-12) Number 12m Minute in hour Number 30s Second in minute Number 55S Millisecond Number 978z Time zone General time zone Pacific Standard Time; PST; GMT-08:00Z Time zone RFC 822 time zone -0800X Time zone ISO 8601 time zone -08; -0800; -08:00
