在
javadoc of java.util.Formatter我读到：
‘m’ Month,formatted as two digits with leading zeros as necessary,
i.e. 01 – 13.
为什么13？
解决方法
Javadoc解释了为什么……
‘m’ ‘\u006d’ Month,i.e. 01 – 13,where “01” is the first month of the year and (“13” is a special value required to support lunar calendars).