记录一下ruby时间格式的处理：
irb>t = Time.now
irb>t.strftime("%Y-%m-%d %H:%M:%S")
=>"2011-10-19 11:07:36"
irb>t.strftime("%d-%b-%Y %I:%M:%S %p")
=>"19-Oct-2011 11:07:36 AM"
irb>t.strftime("at %I:%M%p")
=>"at 11:07AM"

各种参数如下：
%a - The abbreviated weekday name (``Sun'') %A - The full weekday name (``Sunday'') %b - The abbreviated month name (``Jan'') %B - The full month name (``January'') %c - The preferred local date and time representation %d - Day of the month (01..31) %H - Hour of the day, 24-hour clock (00..23) %I - Hour of the day, 12-hour clock (01..12) %j - Day of the year (001..366) %m - Month of the year (01..12) %M - Minute of the hour (00..59) %p - Meridian indicator (``AM'' or ``PM'') %S - Second of the minute (00..60) %U - Week number of the current year, starting with the first Sunday as the first day of the first week (00..53) %W - Week number of the current year, starting with the first Monday as the first day of the first week (00..53) %w - Day of the week (Sunday is 0, 0..6) %x - Preferred representation for the date alone, no time %X - Preferred representation for the time alone, no date %y - Year without a century (00..99) %Y - Year with century %Z - Time zone name %% - Literal ``%'' character http://ruby-doc.org/core/classes/Time.html#M000298