前言
在我们java开发中，Date日期这个字段会被经常使用，比如获取当前系统的时间，获取上个月，上一年的时间，以及获取两个日期相差的时分秒数，或者对日期类型进行格式化，等等，等等，下面将给大家详细介绍下Java中常用时间的一些相关方法
一、获取当前时间的方式
public static void main(String[] args) {
//Date
Date now = new Date();
System.out.println(now);
//java8的时间
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDateTime);
Calendar calendar = Calendar.getInstance();
Date time = calendar.getTime();
System.out.println(time);
System.out.println("年" + calendar.get(Calendar.YEAR));
System.out.println("月" + (calendar.get(Calendar.MONTH) + 1));
//joda time
DateTime dateTime = DateTime.now();
System.out.println(dateTime);
}
获取当前时间可以使用Date LocalDatetime Calendar Datetime
二、获取当月第n天
public static void main(String[] args) {
//建议使用Calendar 可以设置年月日时分秒
Calendar calendar = Calendar.getInstance();
////当月16
calendar.set(Calendar.DAY_OF_MONTH, 16);
System.out.println(calendar.getTime());
//当月16
DateTime now = DateTime.now();
DateTime dateTime = now.withDayOfMonth(16);
System.out.println(dateTime);
//当月14
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println(localDateTime.withDayOfMonth(14));
//1月11
System.out.println(localDateTime.withMonth(1).withDayOfMonth(11));
}
三、格式化为字符串
```
//使用SimpleDateFormat
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println(format.format(new Date()));
//使用Calendar
Calendar calendar = Calendar.getInstance();
System.out.println(String.format("%s年%s月%s日%s时%s分%s秒", calendar.get(Calendar.YEAR),
calendar.get(Calendar.MONTH) + 1, calendar.get(Calendar.DAY_OF_MONTH),
calendar.get(Calendar.HOUR_OF_DAY), calendar.get(Calendar.MINUTE), calendar.get(Calendar.SECOND)));
LocalDateTime now = LocalDateTime.now();
String str = now.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
System.out.println(str);
```
四、加减时间（单位可以是秒，小时等）
public static void main(String[] args) {
Date now = new Date();
//加一小时
long time = now.getTime() + (60 * 60 * 1000);
System.out.println(new Date(time));
//引入Hutool 加一小时
System.out.println(DateUtil.offset(now, DateField.HOUR, 1));
//减一小时
System.out.println(DateUtil.offset(now, DateField.HOUR, -1));
LocalDateTime localDateTime = LocalDateTime.now();
System.out.println("加一小时" + localDateTime.plusHours(1));
System.out.println("减一小时" + localDateTime.minusHours(1));
DateTime dateTime = DateTime.now();
System.out.println(dateTime.plusHours(1));
System.out.println(dateTime.minusHours(1));
}
LocalDateTime和DateTime都自带增加和减少时间的方法
五、通过出生日期获取年龄
public static void main(String[] args) {
//时间1990-12-05
DateTime birthDay = DateTime.now().withYear(1990).withMonthOfYear(10).withDayOfMonth(23);
System.out.println(birthDay);
//获取相差得年 会进行月份和日期比较 如
Years years = Years.yearsBetween(birthDay, new DateTime());
System.out.println(years);
System.out.println(years.getYears());
}
还可以使用年份相减，再比较月，日的方法得到生日
六、判断两个时间段是否覆盖
public static void main(String[] args) {
DateTime now = DateTime.now();
DateTime start1 = now;
DateTime end1 = now.plusMinutes(1);
DateTime start2 = now.plusSeconds(50);
DateTime end2 = now.plusMinutes(2);
Interval interval1 = new Interval(start1, end1);
Interval interval2 = new Interval(start2, end2);
System.out.println(interval1.overlaps(interval2));
System.out.println(start1.getMillis() < end2.getMillis() && start2.getMillis() < end1.getMillis());
}
七、求两个时间间隔
public static void main(String[] args) {
DateTime now = DateTime.now();
//开始时间
Date startTime = now.toDate();
//结束时间
Date endTime = now.plusHours(1).toDate();
//1小时
System.out.println("开始时间与结束时间的时间间隔:" + DateUtil.between(startTime, endTime, DateUnit.SECOND));
long time = (endTime.getTime() - startTime.getTime()) / 1000;
System.out.println(time);
}
八、UTC时间与北京时间转换
public static void main(String[] args) throws ParseException {
Date now = new Date();
Date utcDate = bj2UTC(now);
//utc时间
System.out.println(utcDate);
//北京时间
System.out.println(utc2BJ(utcDate));
DateTime dateTime = DateTime.now().withDayOfMonth(1).withHourOfDay(0).withMinuteOfHour(0).withSecondOfMinute(0);
System.out.println(dateTime);
System.out.println(bj2UTC(dateTime.toDate()));
}
public static Date bj2UTC(Date date) {
if (date == null) {
return null;
}
LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.of("-8"));
return Date.from(localDateTime.atOffset(ZoneOffset.UTC).toInstant());
}
public static Date utc2BJ(Date date) {
if (date == null) {
return null;
}
LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.of("+8"));
return Date.from(localDateTime.atOffset(ZoneOffset.UTC).toInstant());
}
北京时间=UTC+8
总结
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