Formatting
Date and Time Patterns
Date and time formats are specified by date and time pattern strings. Within date and time pattern strings, unquoted letters from 'A' to 'Z' and from 'a' to 'z' are interpreted as pattern letters representing the components of a date or time string. Text can be quoted using single quotes (') to avoid interpretation. "''" represents a single quote. All other characters are not interpreted; they're simply copied into the output string during formatting or matched against the input string during parsing.
The following pattern letters are defined (all other characters from 'A' to 'Z' and from 'a' to 'z' are reserved):
G
Era designator
AD
y
Year
1996; 96
Y
Week year
2009; 09
M
Month in year (context sensitive)
July; Jul; 07
L
Month in year (standalone form)
July; Jul; 07
w
Week in year
27
W
Week in month
2
D
Day in year
189
d
Day in month
10
F
Day of week in month
2
E
Day name in week
Tuesday; Tue
u
Day number of week (1 = Monday, ..., 7 = Sunday)
1
a
Am/pm marker
PM
H
Hour in day (0-23)
0
k
Hour in day (1-24)
24
K
Hour in am/pm (0-11)
0
h
Hour in am/pm (1-12)
12
m
Minute in hour
30
s
Second in minute
55
S
Millisecond
978
z
Time zone
Pacific Standard Time; PST; GMT-08:00
Z
Time zone
-0800
X
Time zone
-08; -0800; -08:00
Examples
The following examples show how date and time patterns are interpreted in the U.S. locale. The given date and time are 2001-07-04 12:08:56 local time in the U.S. Pacific Time time zone.
"yyyy.MM.dd G 'at' HH:mm:ss z"
2001.07.04 AD at 12:08:56 PDT
"EEE, MMM d, ''yy"
Wed, Jul 4, '01
"h:mm a"
12:08 PM
"hh 'o''clock' a, zzzz"
12 o'clock PM, Pacific Daylight Time
"K:mm a, z"
0:08 PM, PDT
"yyyyy.MMMMM.dd GGG hh:mm aaa"
02001.July.04 AD 12:08 PM
"EEE, d MMM yyyy HH:mm:ss Z"
Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ"
010704120856-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSZ"
2001-07-04T12:08:56.235-0700
"yyyy-MM-dd'T'HH:mm:ss.SSSXXX"
2001-07-04T12:08:56.235-07:00
"YYYY-'W'ww-u"
2001-W27-3
reference: https://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html