java8 LocalDateTime

在多并发情况下使用SimpleDateFormat需格外注意：SimpleDateFormat除了format是线程不安全以外，parse方法也是线程不安全的。

LocalDate

只获取年月日

LocalDate localDate = LocalDate.now();  //2020-06-01
LocalDate localDate1 = LocalDate.of(2020, 01, 01); //2020-01-01

获取年、月、日、星期几

int year = localDate.getYear();  //2020
int year1 = localDate.get(ChronoField.YEAR);  //2020
Month month = localDate.getMonth();  //JUNE
int month1 = localDate.get(ChronoField.MONTH_OF_YEAR);  //6
int day = localDate.getDayOfMonth();   //1
int day1 = localDate.get(ChronoField.DAY_OF_MONTH);  //1
DayOfWeek dayOfWeek = localDate.getDayOfWeek();  //MONDAY
int dayOfWeek1 = localDate.get(ChronoField.DAY_OF_WEEK); //1

LocalTime

只获取时分秒

LocalTime localTime = LocalTime.of(23, 11, 11);  //23:11:11
LocalTime localTime1 = LocalTime.now(); //23:15:51.710

获取时分秒

int hour = localTime.getHour();  //23
int hour1 = localTime.get(ChronoField.HOUR_OF_DAY);  //23 
int minute = localTime.getMinute();  //11
int minute1 = localTime.get(ChronoField.MINUTE_OF_HOUR);  //11
int second = localTime.getSecond();  //11
int second1 = localTime.get(ChronoField.SECOND_OF_MINUTE); //11

LocalDateTime

LocalDateTime localDateTime = LocalDateTime.now(); //2020-06-01T23:23:50.559

Instant

获取秒数、获取毫秒数

Instant instant = Instant.now(); //2020-06-01T15:27:18.608Z
long currentSecond = instant.getEpochSecond(); //1591025238
long currentMilli = instant.toEpochMilli(); //1591025238608
System.currentTimeMillis(); //1591025406619

修改

LocalDate localDate = LocalDate.of(2020, 01, 01); //2020-01-01
//增加一年  
localDate = localDate .plusYears(1);  //2021-01-01
localDate = localDate .plus(1, ChronoUnit.YEARS);  //2022-01-01
//减少一年  
localDate = localDate .minusYears(1);  //2021-01-01
localDate = localDate .minus(1, ChronoUnit.YEARS);  //2020-01-01
//增加一个月  
localDate = localDate .plusMonths(1);  //2020-02-01
localDate = localDate .plus(1, ChronoUnit.MONTHS); //2020-03-01
//减少一个月  
localDate = localDate .minusMonths(1);  //2020-02-01
localDate = localDate .minus(1, ChronoUnit.MONTHS); //2020-01-01
//加一天
localDate = localDate .plusDays(1); //2020-01-02
localDate = localDate .plus(1, ChronoUnit.DAYS); //2020-01-03
//减一天
localDate = localDate .minusDays(1); //2020-01-02
localDate = localDate .minus(1, ChronoUnit.DAYS); //2020-01-01

with修改年、月、日

//修改年为2030  
localDate= localDate.withYear(2030  );  //2030-01-01
//修改年为2040
localDate= localDate.with(ChronoField.YEAR, 2040); //2040-01-01
//修改月为8  
localDate= localDate.withMonth(2030  );  //2040-08-01
//修改月为9
localDate= localDate.with(ChronoField.MONTH_OF_YEAR, 9); //2040-09-01
//修改日为7
localDate= localDate.withDayOfMonth(7);  //2040-09-07
//修改日为8
localDate= localDate.with(ChronoField.DAY_OF_MONTH, 8); //2040-09-08

格式化时间

LocalDate localDate = LocalDate.of(2019, 9, 10);  //2019-09-10
String s1 = localDate.format(DateTimeFormatter.BASIC_ISO_DATE);  //20190910
String s2 = localDate.format(DateTimeFormatter.ISO_LOCAL_DATE); //2019-09-10  
//自定义格式化  
DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");  
String s3 = localDate.format(dateTimeFormatter); //10/09/2019