LocalDateTime
java8使用了LocalDateTime和DateTimeFormatter。比之前的Date和Carlendar有所改进。
DateTimeFormatter是线程安全的。DateTimeFormatter中很多属性使用了final修饰。
LocalDate: 只能设置仅含年月日的格式，表示没有时区的日期, LocalDate是不可变并且线程安全的
LocalTime: 只能设置仅含时分秒的格式，表示没有时区的时间, LocalTime是不可变并且线程安全的
LocalDateTime: 可以设置含年月日时分秒的格式 ， 表示没有时区的日期时间, LocalDateTime是不可变并且线程安全的
ZoneId: 时区ID，用来确定Instant和LocalDateTime互相转换的规则
Instant: 用来表示时间线上的一个点（瞬时）
Clock: 用于访问当前时刻、日期、时间，用到时区
Duration: 用秒和纳秒表示时间的数量（长短），用于计算两个日期的“时间”间隔
构建LocalDateTime对象：
public void generateLocalDate() {
LocalDate date = LocalDate.of(2000, 1, 8);
LocalDateTime dateTime = LocalDateTime.of(2020, 1, 8, 15, 16, 17);
System.out.println("date：" + date);
System.out.println("dateTime:" + dateTime);
}
获取LocalDateTime的年月日：
public void getLocalDateTimeMonth() {
LocalDateTime dateTime = LocalDateTime.of(2020, 1, 8, 15, 16, 17);
int year=dateTime.getYear();
int month=dateTime.getMonth().getValue();
int day=dateTime.getDayOfMonth();
System.out.println("dateTime对应的年份为："+year);
System.out.println("dateTime对应的月份为："+month);
System.out.println("dateTime对应的天数为："+day);
}
字符串String转LocalDateTime：
public void stringToTime() {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String datetimeText = "2020-04-01 23:59:59";
LocalDateTime localDateTime = LocalDateTime.parse(datetimeText, formatter);
// LocalDateTime的toString()方法，在日期和时间中间加入了"T"字符串
System.out.println(localDateTime);
}
LocalDateTime 转字符串String：
public void localDateTimeToString() {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime dateTime = LocalDateTime.of(2020, 1, 8, 15, 16, 17);
String dateTimeStr = dateTime.format(formatter);
System.out.println("dateTimeStr为：" + dateTime);
}
LocalDateTime 转时间戳毫秒
public static long getMillsByLocalDateTime(LocalDateTime localDateTime) {
long mills = localDateTime.toInstant(ZoneOffset.of("+8")).toEpochMilli();
return mills;
}
时间戳毫秒转LocalDateTime
public static LocalDateTime getLocalDateTimeByMills() {
long mills = 1640419285000L;
LocalDateTime result = new Date(mills).toInstant().atOffset(ZoneOffset.of("+8")).toLocalDateTime();
return result;
}
Date转Instant：
Instant instant= date.toInstant();
Instant转Date：
Date date = Date.from(instant);
Date转LocalDateTime ：
public static void dateToLocalDateTime(Date date) {
Instant dateInstant = date.toInstant();
LocalDateTime localDateTime = LocalDateTime.ofInstant(dateInstant, ZoneId.systemDefault());
}
LocalDateTime转Date：
public static Date parse(LocalDateTime localDateTime) {
return Date.from(localDateTime.atZone( ZoneId.systemDefault()).toInstant());
}
LocalDateTime 获取LocalDate：
LocalDate localDate = localDateTime.toLocalDate();
LocalDateTime 获取LocalTime：
LocalTime localTime = localDateTime.toLocalTime();
LocalDate
Date转LocalDate：
public void dateToLocalDate(Date date) {
Instant dateInstant = date.toInstant();
LocalDate localDate = LocalDateTime.ofInstant(dateInstant, ZoneId.systemDefault()).toLocalDate();
}
LocalDate转Date：
public static Date parse(LocalDate localDate) {
return Date.from(localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant());
}
localDate转String ：
public static String localDateToString(Date date) {
Instant dateInstant = date.toInstant();
LocalDate localDate = LocalDateTime.ofInstant(dateInstant, ZoneId.systemDefault()).toLocalDate();
// localDate转String
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String localDateStr = localDate.format(formatter);
System.out.println(localDateStr);
return localDateStr;
}
String转LocalDate：
public static void stringToLocalDate() {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String datetimeText = "2020-04-01";
LocalDate localDate = LocalDate.parse(datetimeText, formatter);
System.out.println(localDate);
}
LocalDate获取年月日:
int year = localDate.getYear();
int monthValue = localDate.getMonthValue();
int dayOfMonth = localDate.getDayOfMonth();
LocalDate修改年月日：
public static void changeYearMonthDay() {
LocalDate localDate = LocalDate.now();
//修改年份
LocalDate withYearResult = localDate.withYear(2020);
//修改月份
LocalDate withMonthResult = localDate.withMonth(5);
//修改日
LocalDate withDayResult = localDate.withDayOfMonth(20);
System.out.println( withYearResult + "，" + withMonthResult+ "，"+ withDayResult);
}
LocalDate比较日期大小compareTo：
compareTo()方法
在两边相等（=）的情况下返回 0
在左边大于（>）右边时返回 1
在左边小于（<）右边时返回 -1
public static void localDateCompareTo() {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String datetimeText = "2020-04-01";
LocalDate localDate = LocalDate.parse(datetimeText, formatter);
LocalDate nowDate = LocalDate.now();
System.out.println(localDate);
System.out.println("nowDate:"+nowDate);
if (nowDate.compareTo(localDate) < 0) {
System.out.println("nowDate小于"+ datetimeText);
} else {
System.out.println("nowDate大于等于"+ datetimeText);
}
}
LocalDate比较日期的前后：
after 只在大于（>）情况下才为true (相等时不会）
before 只在小于（<）情况下才为true (相等时不会）
public static void isBeforeAfter() {
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String datetimeText = "2020-04-01";
LocalDate localDate = LocalDate.parse(datetimeText, formatter);
LocalDate nowDate = LocalDate.now();
System.out.println(localDate);
System.out.println("nowDate:"+nowDate);
if (nowDate.isBefore(localDate)) {
System.out.println(nowDate+ "在"+ datetimeText +"之前");
} else {
System.out.println(nowDate+ "在"+ datetimeText +"之后");
}
}
获取日期差距 / 获取日期时间间隔 ：
public static void durationDateTime() {
LocalDateTime date3 = LocalDateTime.now();
LocalDateTime date4 = LocalDateTime.of(2018, 1, 13, 22, 30, 10);
Duration duration = Duration.between(date3, date4);
System.out.println(date3 + " 与 " + date4 + " 间隔 " + "\n"
+ " 天 :" + duration.toDays() + "\n"
+ " 时 :" + duration.toHours() + "\n"
+ " 分 :" + duration.toMinutes() + "\n"
+ " 毫秒 :" + duration.toMillis() + "\n"
+ " 纳秒 :" + duration.toNanos() + "\n"
);
}
日期时间计算：
public void addMonthDay() {
LocalDateTime dt = LocalDateTime.of(2020, 1, 26, 20, 30, 59);
System.out.println(dt);
// 加5天减3小时:
LocalDateTime dt2 = dt.plusDays(5).minusHours(3);
System.out.println(dt2); // 2019-10-31T17:30:59
// 减1月:
LocalDateTime dt3 = dt2.minusMonths(1);
System.out.println(dt3); // 2019-09-30T17:30:59
}
LocalTime
LocalTime获取时分秒：
//获取小时
int hour = localTime.getHour();
int hour1 = localTime.get(ChronoField.HOUR_OF_DAY);
//获取分
int minute = localTime.getMinute();
int minute1 = localTime.get(ChronoField.MINUTE_OF_HOUR);
//获取秒
int second = localTime.getMinute();
int second1 = localTime.get(ChronoField.SECOND_OF_MINUTE);
参考资料：
https://www.liaoxuefeng.com/wiki/1252599548343744/1303871087444002
https://blog.csdn.net/weixin_38405253/article/details/100765007
https://www.jianshu.com/p/048ee8580639
