功能说明：
Pattern Description
Y,YYY year (4 or more digits) with a comma
YYYY year (4 or more digits)
YYY last 3 digits of year
YY last 2 digits of year
Y last digit of year
IYYY ISO 8601 week-numbering year
IYY last 3 digits of ISO 8601 week-numbering year
IY last 2 digits of ISO 8601 week-numbering year
I last digit of ISO 8601 week-numbering year
BC, bc, AD, or ad era indicator without periods
B.C., b.c., A.D. or a.d. era indicator with periods
MONTH full upper case month name (blank-padded to 9 characters)
Month full capitalised month name (blank-padded to 9 characters)
month full lower case month name (blank-padded to 9 characters)
MON abbreviated upper case month name
Mon abbreviated capitalised month name
mon abbreviated lower case month name
MM month number (01-12)
DAY full upper case day name (blank-padded to 9 characters)
Day full capitalised day name (blank-padded to 9 characters)
day full lower case day name (blank-padded to 9 characters)
DY abbreviated upper case day name (blank-padded to 9 characters)
Dy abbreviated capitalised day name (blank-padded to 9 characters)
dy abbreviated lower case day name (blank-padded to 9 characters)
DDD day of year (001-366)
IDDD day of ISO 8601 week-numbering year (001-371). Day 1 of the year is Monday of the first ISO week
DD day of month (01-31)
D day of the week, Sunday (1) to Saturday (7)
ID ISO 8601 day of the week, Monday (1) to Sunday (7)
W week of the month (1-5). The first week starts on the first day of the month
WW week number of the year (1-53). The first week starts on the first day of the year
IW week number of ISO 8601 week-numbering year (01-53). The first Thursday of the year is in week 1.
CC 2 digit century (the 21st century starts on 2001-01-01)
J Julian Date (number of days since Nov 24, 4714 BC)
Q quarter
RM month in upper case Roman numerals (I-XII, I=January)
rm month in lower case Roman numerals (i-xii, i=January)