日程
Recurrence Rules（rrules）
资料
RFC 5545 - Internet Calendaring and Scheduling Core Object Specification (iCalendar)（RFC5545 中文翻译 ）
iCalendar.org - iCalendar.org - iCalendar Resources, Specifications and Tools
Events | Google Calendar | Google for Developers
库
ical4j/ical4j: A Java library for parsing and building iCalendar data models