伴随 lambda表达式、streams 以及一系列小优化，Java 8 推出了全新的日期时间API。 Java处理日期、日历和时间的不足之处：将 java.util.Date 设定为可变类型，以及 SimpleDateFormat 的非线程安全使其应用非常受限。然后就在 java8 上面增加新的特性。 全新API的众多好处之一就是，明确了日期时间概念，例如：瞬时（instant）、 长短（duration）、日期、时间、时区和周期。 同时继承了Joda 库按人类语言和计算机各自解析的时间处理方式。不同于老版本，新API基于ISO标准日历系统，java.time包下的所有类都是不可变类型而且线程安全。
import java.time.Clock; import java.time.Instant; import java.time.LocalDate; import java.time.LocalDateTime; import java.time.LocalTime; import java.time.Month; import java.time.MonthDay; import java.time.OffsetDateTime; import java.time.ZoneOffset; import java.time.Period; import java.time.YearMonth; import java.time.ZoneId; import java.time.ZonedDateTime; import java.time.format.DateTimeFormatter; import java.time.temporal.ChronoUnit; import java.util.Date; public class DateTest { //获取今天的日期 public void getCurrentDate(){ LocalDate today = LocalDate.now(); System.out.println("Today's Local date : " + today); //这个是作为对比 Date date = new Date(); System.out.println(date); } //获取年、月、日信息 public void getDetailDate(){ LocalDate today = LocalDate.now(); int year = today.getYear(); int month = today.getMonthValue(); int day = today.getDayOfMonth(); System.out.printf("Year : %d Month : %d day : %d t %n", year, month, day); } //处理特定日期 public void handleSpecilDate(){ LocalDate dateOfBirth = LocalDate.of(2018, 01, 21); System.out.println("The specil date is : " + dateOfBirth); } //判断两个日期是否相等 public void compareDate(){ LocalDate today = LocalDate.now(); LocalDate date1 = LocalDate.of(2018, 01, 21); if(date1.equals(today)){ System.out.printf("TODAY %s and DATE1 %s are same date %n", today, date1); } } //处理周期性的日期 public void cycleDate(){ LocalDate today = LocalDate.now(); LocalDate dateOfBirth = LocalDate.of(2018, 01, 21); MonthDay birthday = MonthDay.of(dateOfBirth.getMonth(), dateOfBirth.getDayOfMonth()); MonthDay currentMonthDay = MonthDay.from(today); if(currentMonthDay.equals(birthday)){ System.out.println("Many Many happy returns of the day !!"); }else{ System.out.println("Sorry, today is not your birthday"); } } //获取当前时间 public void getCurrentTime(){ LocalTime time = LocalTime.now(); System.out.println("local time now : " + time); } //增加小时 public void plusHours(){ LocalTime time = LocalTime.now(); LocalTime newTime = time.plusHours(2); // 增加两小时 System.out.println("Time after 2 hours : " + newTime); } //如何计算一周后的日期 public void nextWeek(){ LocalDate today = LocalDate.now(); LocalDate nextWeek = today.plus(1, ChronoUnit.WEEKS); System.out.println("Today is : " + today); System.out.println("Date after 1 week : " + nextWeek); } //计算一年前或一年后的日期 public void minusDate(){ LocalDate today = LocalDate.now(); LocalDate previousYear = today.minus(1, ChronoUnit.YEARS); System.out.println("Date before 1 year : " + previousYear); LocalDate nextYear = today.plus(1, ChronoUnit.YEARS); System.out.println("Date after 1 year : " + nextYear); } public void clock(){ // 根据系统时间返回当前时间并设置为UTC。 Clock clock = Clock.systemUTC(); System.out.println("Clock : " + clock); // 根据系统时钟区域返回时间 Clock defaultClock = Clock.systemDefaultZone(); System.out.println("Clock : " + clock); } //如何用Java判断日期是早于还是晚于另一个日期 public void isBeforeOrIsAfter(){ LocalDate today = LocalDate.now(); LocalDate tomorrow = LocalDate.of(2018, 1, 29); if(tomorrow.isAfter(today)){ System.out.println("Tomorrow comes after today"); } LocalDate yesterday = today.minus(1, ChronoUnit.DAYS); if(yesterday.isBefore(today)){ System.out.println("Yesterday is day before today"); } } //时区处理 public void getZoneTime(){ //设置时区 ZoneId america = ZoneId.of("America/New_York"); LocalDateTime localtDateAndTime = LocalDateTime.now(); ZonedDateTime dateAndTimeInNewYork = ZonedDateTime.of(localtDateAndTime, america ); System.out.println("现在的日期和时间在特定的时区 : " + dateAndTimeInNewYork); } //使用 YearMonth类处理特定的日期 public void checkCardExpiry(){ YearMonth currentYearMonth = YearMonth.now(); System.out.printf("Days in month year %s: %d%n", currentYearMonth, currentYearMonth.lengthOfMonth()); YearMonth creditCardExpiry = YearMonth.of(2028, Month.FEBRUARY); System.out.printf("Your credit card expires on %s %n", creditCardExpiry); } //检查闰年 public void isLeapYear(){ LocalDate today = LocalDate.now(); if(today.isLeapYear()){ System.out.println("This year is Leap year"); }else { System.out.println("2018 is not a Leap year"); } } //计算两个日期之间的天数和月数 public void calcDateDays(){ LocalDate today = LocalDate.now(); LocalDate java8Release = LocalDate.of(2018, Month.MAY, 14); Period periodToNextJavaRelease = Period.between(today, java8Release); System.out.println("Months left between today and Java 8 release : " + periodToNextJavaRelease.getMonths() ); } // 包含时差信息的日期和时间 public void ZoneOffset(){ LocalDateTime datetime = LocalDateTime.of(2018, Month.FEBRUARY, 14, 19, 30); ZoneOffset offset = ZoneOffset.of("+05:30"); OffsetDateTime date = OffsetDateTime.of(datetime, offset); System.out.println("Date and Time with timezone offset in Java : " + date); } // 获取时间戳 public void getTimestamp(){ Instant timestamp = Instant.now(); System.out.println("What is value of this instant " + timestamp); } // 使用预定义的格式化工具去解析或格式化日期 public void formateDate(){ String dayAfterTommorrow = "20180210"; LocalDate formatted = LocalDate.parse(dayAfterTommorrow, DateTimeFormatter.BASIC_ISO_DATE); System.out.printf("Date generated from String %s is %s %n", dayAfterTommorrow, formatted); } public static void main(String[] args) { DateTest dt = new DateTest(); dt.formateDate(); } }