SimpleDateFormat

1. java.text.SimpleDateFormat - 日期格式处理类
2. 线程不安全的类.

目标

1. Date类型转换成String类型 - 按照指定的日期格式.

   //pattern必须是一个有效的格式化模板,如果传入了一个非法模板
   //那么就会抛出一个java.lang.IllegalArgumentException - 非法参数异常
   // Illegal pattern character 'q'
   String format(Date date);
   

2. String类型转换成Date类型.

   //如果构造中的pattern的格式和日期的字符串的格式不一致,那么在调用
   //parse方法的时候就会抛出java.text.ParseException: Unparseable date: "2020-09-03"
   //解析失败异常
   Date parse(String str);
   

模板pattern

Letter	Date or Time Component	Presentation	Examples
G	Era designator	Text	AD
y	Year	Year	1996; 96
Y	Week year	Year	2009; 09
M	Month in year (context sensitive)	Month	July; Jul; 07
L	Month in year (standalone form)	Month	July; Jul; 07
w	Week in year	Number	27
W	Week in month	Number	2
D	Day in year	Number	189
d	Day in month	Number	10
F	Day of week in month	Number	2
E	Day name in week	Text	Tuesday; Tue
u	Day number of week (1 = Monday, …, 7 = Sunday)	Number	1
a	Am/pm marker	Text	PM
H	Hour in day (0-23)	Number	0
k	Hour in day (1-24)	Number	24
K	Hour in am/pm (0-11)	Number	0
h	Hour in am/pm (1-12)	Number	12
m	Minute in hour	Number	30
s	Second in minute	Number	55
S	Millisecond	Number	978
z	Time zone	General time zone	Pacific Standard Time; PST; GMT-08:00
Z	Time zone	RFC 822 time zone	-0800
X	Time zone	ISO 8601 time zone	-08; -0800; -08:00

日期工具类

java.util.Date