ruby 时间日期处理
1.当前时间
Time.new 或Time.now
2.Time类的方法mktime(同义方法是local方法)来根据传入的参数生成时间对象，并且它使用的是当前的时间
now = Time.now => Sat Mar 05 17:09:55 +0800 2011 now.to_date => Sat, 05 Mar 2011 now.to_s => "Sat Mar 05 17:09:55 +0800 2011" now.to_s(:short) => "05 Mar 17:09" now.to_s(:long) => "March 05, 2011 17:09" now.to_s(:db) => "2011-03-05 17:09:55" now.to_s(:rfc822) => "Sat, 05 Mar 2011 17:09:55 +0800" now.at_beginning_of_day => Sat Mar 05 00:00:00 +0800 2011 now.at_beginning_of_month => Tue Mar 01 00:00:00 +0800 2011 now.at_beginning_of_week => Mon Feb 28 00:00:00 +0800 2011 now.at_beginning_of_quarter => Sat Jan 01 00:00:00 +0800 2011 now.at_beginning_of_year => Sat Jan 01 00:00:00 +0800 2011 now.at_midnight => Sat Mar 05 00:00:00 +0800 2011 now.change(:hour => 13) => Sat Mar 05 13:00:00 +0800 2011 now.last_month => Sat Feb 05 17:09:55 +0800 2011 now.last_year => Fri Mar 05 17:09:55 +0800 2010 now.midnight => Sat Mar 05 00:00:00 +0800 2011 now.monday => Mon Feb 28 00:00:00 +0800 2011 now.months_ago(2) => Wed Jan 05 17:09:55 +0800 2011 now.months_ago(1) => Sat Feb 05 17:09:55 +0800 2011 now.months_ago(3) => Sun Dec 05 17:09:55 +0800 2010 now.months_since(2) => Thu May 05 17:09:55 +0800 2011 now.next_week => Mon Mar 07 00:00:00 +0800 2011 now.next_year => Mon Mar 05 17:09:55 +0800 2012 now.seconds_since_midnight => 61795.249 now.since(7200) => Sat Mar 05 19:09:55 +0800 2011 now.tomorrow => Sun Mar 06 17:09:55 +0800 2011 now.years_ago(2) => Thu Mar 05 17:09:55 +0800 2009 now.years_since(2) => Tue Mar 05 17:09:55 +0800 2013 now.yesterday=> Fri Mar 04 17:09:55 +0800 2011 now.advance(:days => 30) => Mon Apr 04 17:09:55 +0800 2011 Time.days_in_month(2) => 28 Time.days_in_month(2,2000) => 29
