以前操作时间都是使用SimpleDateFormat类改变Date的时间格式，使用Calendar类操作时间。但是SimpleDateFormat是线程不安全的，源码如下：
private StringBuffer format(Date date, StringBuffer toAppendTo,
FieldDelegate delegate) {
// Convert input date to time field list
calendar.setTime(date); boolean useDateFormatSymbols = useDateFormatSymbols(); for (int i = 0; i < compiledPattern.length; ) {
int tag = compiledPattern[i] >>> 8;
int count = compiledPattern[i++] & 0xff;
if (count == 255) {
count = compiledPattern[i++] << 16;
count |= compiledPattern[i++];
} switch (tag) {
case TAG_QUOTE_ASCII_CHAR:
toAppendTo.append((char)count);
break; case TAG_QUOTE_CHARS:
toAppendTo.append(compiledPattern, i, count);
i += count;
break; default:
subFormat(tag, count, delegate, toAppendTo, useDateFormatSymbols);
break;
}
}
return toAppendTo;
}
calendar是共享变量，并且这个共享变量没有做线程安全控制。当多个线程同时使用相同的SimpleDateFormat对象调用format方法时，多个线程会同时调用calendar.setTime方法，可能一个线程刚设置好time值另外的一个线程马上把设置的time值给修改了导致返回的格式化时间可能是错误的。
所以JAVA8推出了LocalDate、LocalTime、LocalDateTime是线程安全、简易、高可靠的时间包。源码如下
-
LocalDate 获取年月日
@Test
public void localDataTest(){
//创建LocalDate获取当前年月日
LocalDate now = LocalDate.now();
System.out.println("当前时间：" + now);
//构造指定的年月日
LocalDate localDate = LocalDate.of(2020, 11, 24);
System.out.println("当前指定时间：" + localDate);
int year = now.getYear();
System.out.println("当前年year：" + year);
int year1 = now.get(ChronoField.YEAR);
System.out.println("当前年year1：" + year1);
Month month = now.getMonth();
System.out.println("当前月month：" + month);
int month1 = now.get(ChronoField.MONTH_OF_YEAR);
System.out.println("当前月month1：" + month1);
int day = now.getDayOfMonth();
System.out.println("当前天day：" + day);
int day1 = now.get(ChronoField.DAY_OF_MONTH);
System.out.println("当前天day1：" + day1);
DayOfWeek dayOfWeek = now.getDayOfWeek();
System.out.println("当前星期几dayOfWeek：" + dayOfWeek);
int dayOfWeek1 = now.get(ChronoField.DAY_OF_WEEK);
System.out.println("当前星期几dayOfWeek1：" + dayOfWeek1);
} -
LocalTime 获取时分秒
@Test
public void localTimeTest(){
//创建LocalTime获取当前时分秒
LocalTime now = LocalTime.now();
System.out.println("当前时间：" + now);
LocalTime localTime = LocalTime.of(13, 51, 10);
System.out.println("指定时间：" + localTime);
int hour = now.getHour();
System.out.println("当前小时数hour："+ hour);
int hour1 = now.get(ChronoField.HOUR_OF_DAY);
System.out.println("当前小时数hour1："+ hour1);
int minute = now.getMinute();
System.out.println("当前分钟数minute："+ minute);
int minute1 = now.get(ChronoField.MINUTE_OF_DAY);
System.out.println("当前分钟数minute1："+ minute1);
int second = now.getSecond();
System.out.println("当前秒数second："+ second);
int second1 = now.get(ChronoField.SECOND_OF_MINUTE);
System.out.println("当前秒数second1："+ second1);
} -
LocalDateTime 获取年月日时分秒，相当于LocalDate+LocalTime，可与LocalDate、LocalTime相互转换
@Test
public void localDataTimeTest(){
//创建localDateTime获取当前年月日时分秒
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println("当前时间：" + localDateTime);
LocalDateTime localDateTime1 = LocalDateTime.of(2020, Month.SEPTEMBER, 10, 14, 46, 56);
System.out.println("指定时间：" + localDateTime1);
LocalDateTime of = LocalDateTime.of(LocalDate.now(), LocalTime.now());
System.out.println("当前时间1：" + of);
LocalDateTime localDateTime2 = LocalDate.now().atTime(LocalTime.now());
System.out.println("当前时间2：" + localDateTime2);
LocalDateTime localDateTime3 = LocalTime.now().atDate(LocalDate.now());
System.out.println("当前时间3：" + localDateTime3);
LocalDate localDate = localDateTime.toLocalDate();
System.out.println("当前年月日：" + localDate);
LocalTime localTime = localDateTime.toLocalTime();
System.out.println("当前时分秒：" + localTime); } -
Period 时间长度类 Period表示以年、月、日衡量的时长，通过Period增加、减少年月日
@Test
public void periodTest(){
//创建localDateTime获取当前年月日时分秒
LocalDateTime localDateTime = LocalDateTime.now();
//创建Period对象，设置一年
Period period = Period.ofYears(1);
//增加一年
LocalDate localDate = localDateTime.toLocalDate().plus(period);
System.out.println("增加一年后的时间：" + localDate);
Period period1 = Period.ofYears(-1);
//减少一年
LocalDate localDate1 = localDateTime.toLocalDate().plus(period1);
System.out.println("减少一年后的时间：" + localDate1);
//创建Period对象，设置一月
Period period2 = Period.ofMonths(1);
//增加一个月
LocalDate localDate2 = localDateTime.toLocalDate().plus(period2);
System.out.println("增加一个月后的时间：" + localDate2);
//创建Period对象，设置一周
Period period3 = Period.ofWeeks(1);
//增加一周
LocalDate localDate3 = localDateTime.toLocalDate().plus(period3);
System.out.println("增加一周后的时间：" + localDate3);
//创建Period对象，设置一天
Period period4 = Period.ofDays(1);
//增加一天
LocalDate localDate4 = localDateTime.toLocalDate().plus(period4);
System.out.println("增加一天后的时间：" + localDate4);
} -
Duration 时间长度类 Duration表示以时、分、秒衡量的时长，通过Duration增加、减少时分秒
@Test
public void durationTest(){
//创建localDateTime获取当前时间时分秒
LocalDateTime localDateTime = LocalDateTime.now();
//创建Duration对象，设置1天
Duration duration = Duration.ofDays(1);
//增加一天
LocalTime localTime = localDateTime.toLocalTime().plus(duration);
System.out.println("增加一天后时间：" + localTime);
//创建Duration对象，设置一小时
Duration duration1 = Duration.ofHours(-1);
//减少一天
LocalTime localTime1 = localDateTime.toLocalTime().plus(duration1);
System.out.println("增加一天后时间：" + localTime1);
//创建Duration对象，设置一小时
Duration duration2 = Duration.ofHours(1);
//增加一小时
LocalTime localTime2 = localDateTime.toLocalTime().plus(duration2);
System.out.println("增加一小时后时间：" + localTime2);
//创建Duration对象，设置一分钟
Duration duration3 = Duration.ofMinutes(1);
//增加一分钟
LocalTime localTime3 = localDateTime.toLocalTime().plus(duration3);
System.out.println("增加一分钟后时间：" + localTime3);
//创建Duration对象，设置十秒钟
Duration duration4 = Duration.ofSeconds(10);
//增加十秒钟
LocalTime localTime4 = localDateTime.toLocalTime().plus(duration4);
System.out.println("增加十秒钟后时间：" + localTime4);
//创建Duration对象，设置一百毫秒
Duration duration5 = Duration.ofMillis(100);
//增加一百毫秒
LocalTime localTime5 = localDateTime.toLocalTime().plus(duration5);
System.out.println("增加一百毫秒后时间：" + localTime5);
} -
ZonedDateTime 时区处理类 可以设置时区
@Test
public void zonedDateTimeTest(){
ZoneId zoneId = ZoneId.of("UTC+1");
//设置指定时间、时区
ZonedDateTime zonedDateTime = ZonedDateTime.of(2020, 11, 24, 15, 29, 53, 1026, zoneId);
//获取今天是今年第几天
int dayOfYear = zonedDateTime.getDayOfYear();
System.out.println("今天是今年第"+dayOfYear+"天");
//获取今天是这月第几天
int dayOfMonth = zonedDateTime.getDayOfMonth();
System.out.println("今天是这月第"+dayOfMonth+"天");
//获取今天是这周第几天
int dayOfWeek = zonedDateTime.getDayOfWeek().get(ChronoField.DAY_OF_WEEK);
System.out.println("今天是这周第"+dayOfWeek+"天");
//增加一年
ZonedDateTime zonedDateTime1 = zonedDateTime.plusYears(1);
System.out.println("增加一年后的时间："+zonedDateTime1);
//减少一年
ZonedDateTime zonedDateTime2 = zonedDateTime.minusYears(1);
System.out.println("减少一年后的时间："+zonedDateTime2); }