简介
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。
关键类
Instant：瞬时实例。
LocalDate：本地日期，不包含具体时间 例如：2014-01-14 可以用来记录生日、纪念日、加盟日等。
LocalTime：本地时间，不包含日期。
LocalDateTime：组合了日期和时间，但不包含时差和时区信息。
ZonedDateTime：最完整的日期时间，包含时区和相对UTC或格林威治的时差。
新API还引入了 ZoneOffSet 和 ZoneId 类，使得解决时区问题更为简便。解析、格式化时间的 DateTimeFormatter 类也全部重新设计。
package com.wq.study.java8.date;
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();
}
}