最开始的时候,Date既要承载日期信息,又要做日期之间的转换,还要做不同日期格式的显示,职责较繁杂;后来从JDK1.1开始,这三项职责分开了
java.util.Date与java.util.Calendar中的所有属性都是可变的,下面的代码,计算两个日期之间的天数…
// 计算两个日期之间的天数
private static long daysBetween(Calendar begin, Calendar end) {
long daysBetween = 0;
while (begin.before(end)) {
begin.add(Calendar.DAY_OF_MONTH, 1);
daysBetween++;
}
return daysBetween;
}
Main方法
Calendar birth = Calendar.getInstance();
birth.set(1975, Calendar.MAY, 26);
Calendar now = Calendar.getInstance();
System.out.println(daysBetween(birth, now));
System.out.println(daysBetween(birth, now));
daysBetween有点问题,如果连续计算两个Date实例的话,第二次会取得0,因为Calendar状态是可变的,考虑到重复计算的场合,最好复制一个新的Calendar
SimpleDateTimeFormat是非线程安全的
Java8仍然延用了ISO的日历体系,并且与它的前辈们不同,java.time包中的类是不可变且线程安全的。新的时间及日期API位于java.time包中,下面是里面的一些关键的类:
改包的API提供了大量相关的方法,这些方法一般有一致的方法前缀
public class TimeIntroduction {
public static void main(String[] args) throws InterruptedException {
testClock();
System.out.println("===============================");
testInstant();
System.out.println("===============================");
testLocalDateTime();
System.out.println("===============================");
testNewOldDateConversion();
System.out.println("===============================");
testChronology();
}
static void testClock() throws InterruptedException {
// 时钟提供给我们用于访问某个特定时区的瞬时时间、日期和时间
Clock c1 = Clock.systemUTC();
System.out.println("系统默认UTC时钟(当前瞬时时间 System.currentTimeMillis(): " + c1.millis()); // 系统默认UTC时钟(当前瞬时时间 System.currentTimeMillis())
System.out.println("系统默认UTC时钟(当前瞬时时间 System.currentTimeMillis(): " + System.currentTimeMillis());
Clock c2 = Clock.systemDefaultZone();// 系统默认时区时钟(当前瞬时时间)
System.out.println(" 系统默认时区时钟(当前瞬时时间): " + c2.millis());
Clock c31 = Clock.system(ZoneId.of("Europe/Paris"));//巴黎时区
System.out.println("巴黎时区:" + c31.millis());
Clock c32 = Clock.system(ZoneId.of("Asia/Shanghai"));
System.out.println("上海时区: " + c32.millis());
Clock c4 = Clock.fixed(Instant.now(), ZoneId.of("Asia/Shanghai"));// 固定上海时区时钟
System.out.println("固定上海时区时钟: " + c4.millis());
TimeUnit.MILLISECONDS.sleep(1000);
System.out.println("一秒钟之后,固定上海时区时钟:" + c4.millis()); // 不变,即时钟在那一个点不动
Clock c5 = Clock.offset(c1, Duration.ofSeconds(2));// 相对于系统默认时钟两秒的时钟
System.out.println(c1.millis());
System.out.println(c5.millis());
}
static void testInstant() throws InterruptedException {
// 瞬时时间,相当于以前的System.currentTimeMillis
Instant instant1 = Instant.now();
System.out.println("精确到秒: " + instant1.getEpochSecond());// 精确到秒 得到相对于1970-01-01 00:00:00 UTC的一个时
System.out.println("精确到毫秒:" + instant1.toEpochMilli());// 精确到毫秒
Clock clock1 = Clock.systemUTC();// 获得系统UTC默认时钟
Instant instant2 = Instant.now(clock1);// 得到时钟的瞬时时间
System.out.println("精确到毫秒: " + instant2.toEpochMilli());
Clock clock2 = Clock.fixed(instant1, ZoneId.systemDefault());// 固定瞬时时间时钟
TimeUnit.MILLISECONDS.sleep(2000);
Instant instant3 = Instant.now(clock2);// 得到时钟的瞬时时间
System.out.println("精确到毫秒: " + instant3.toEpochMilli());
}
static void testLocalDateTime() {
// 使用默认时区时钟瞬时时间创建 Clock.systemDefaultZone() --> 即相对于 ZoneId.systemDefault() 默认时区
LocalDateTime now = LocalDateTime.now();
System.out.println(now);
LocalDateTime now2 = LocalDateTime.now(ZoneId.of("Europe/Paris"));
System.out.println(now2);// 会以响应的时区显示日期
// 自定义时钟
Clock clock = Clock.system(ZoneId.of("Asia/Dhaka"));
LocalDateTime now3 = LocalDateTime.now(clock);
System.out.println(now3);// 会以相应的时区显示日期
LocalDateTime d1 = LocalDateTime.of(2013, 12, 31, 23, 59);
LocalDateTime d2 = LocalDateTime.of(2013, 12, 31, 23, 59, 59, 11);
// 使用瞬时时间+时区
Instant instant = Instant.now();
LocalDateTime d3 = LocalDateTime.ofInstant(Instant.now(), ZoneId.systemDefault());
System.out.println(d3);
LocalDateTime d4 = LocalDateTime.parse("2013-12-31T23:59");
System.out.println(d4);
LocalDateTime d5 = LocalDateTime.parse("2013-12-31T23:59:59.999");
System.out.println(d5);
//使用DateTimeFormatter API 解析 和 格式化
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
LocalDateTime d6 = LocalDateTime.parse("2013/12/31 23:59:59", formatter);
System.out.println(formatter.format(d6));
//时间获取
System.out.println(d6.getYear());
System.out.println(d6.getMonth());
System.out.println(d6.getDayOfYear());
System.out.println(d6.getDayOfMonth());
System.out.println(d6.getDayOfWeek());
System.out.println(d6.getHour());
System.out.println(d6.getMinute());
System.out.println(d6.getSecond());
System.out.println(d6.getNano());
//时间增减
LocalDateTime d7 = d6.minusDays(1);
LocalDateTime d8 = d7.plus(1, IsoFields.QUARTER_YEARS);
//LocalDate 即年月日 无时分秒
//LocalTime即时分秒 无年月日
//API和LocalDateTime类似就不演示了
// 两个日期是否相等
System.out.println(d1.equals(d2));
// MonthDay - 用来检查生日
LocalDate dateOfBirth = LocalDate.of(2010, 01, 14);
MonthDay birthday = MonthDay.of(dateOfBirth.getMonth(), dateOfBirth.getDayOfMonth());
MonthDay currentMonthDay = MonthDay.from(ZonedDateTime.now());
System.out.println(currentMonthDay.equals(birthday));
// YearMonth - 用来检查信用卡过期
YearMonth currentYearMonth = YearMonth.now(); System.out.printf("Days in month year %s: %d%n", currentYearMonth, currentYearMonth.lengthOfMonth());
YearMonth creditCardExpiry = YearMonth.of(2018, Month.FEBRUARY);
System.out.printf("Your credit card expires on %s %n", creditCardExpiry);
// 判断闰年 - LocalDate类有一个isLeapYear()的方法
System.out.println(dateOfBirth.isLeapYear());
}
static void testNewOldDateConversion() {
Instant instant = new Date().toInstant();
Date date = Date.from(instant);
System.out.println(instant);
System.out.println(date);
}
// 提供对java.util.Calendar的替换,提供对年历系统的支持
static void testChronology() {
HijrahChronology instance = HijrahChronology.INSTANCE;
ChronoLocalDateTime d = instance.localDateTime(LocalDateTime.now());
System.out.println(d);
}
// 根据指定formatter类型转换 ”yyyy-MM-dd'T'HH:mm:ss.SSSZ “
public static String transToFormatterDate(String date, String formatter) {
LocalDateTime localDate = LocalDateTime.parse(date,DateTimeFormatter.ISO_OFFSET_DATE_TIME);
return localDate.format(DateTimeFormatter.ofPattern(formatter));
}
}