一.为什么使用java8
1.java.util.Date缺点： （1）年份是从1970开始算的； （2）DateFormat方法不是线程安全的。
package newDataApi; import java.text.SimpleDateFormat; import java.util.ArrayList; import java.util.Date; import java.util.List; import java.util.concurrent.*; //SimpleDateFormat线程不安全 public class TestSimpleDateFormat { public static void main(String[] args) throws ExecutionException, InterruptedException { SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMdd"); Callable<Date> task = new Callable<Date>() { @Override public Date call() throws Exception { return simpleDateFormat.parse("20161218" ); } }; ExecutorService pool = Executors.newFixedThreadPool(10); List<Future<Date>> results = new ArrayList<>(); for (int i = 0; i < 10; i++) { results.add(pool.submit(task)); } for (Future<Date> future : results){ System.out.println(future.get()); } } }出现问题： 2.java.util.Calendar缺点： 和Date类一样都是可变的。而且经常会同时用Date和Calendar，很混乱。
3.只有提供一些常用的功能
二.源码
package newDataApi; import java.time.*; import java.time.format.DateTimeFormatter; import java.time.temporal.TemporalAdjuster; import java.time.temporal.TemporalAdjusters; import java.util.Set; public class TestLocalDateTime { public static void main(String[] args) throws InterruptedException { TestLocalDateTime tldt = new TestLocalDateTime(); tldt.test1(); System.out.println("___"); tldt.test2(); System.out.println("___"); tldt.test3(); System.out.println("____"); tldt.test4(); System.out.println("____"); tldt.test5(); System.out.println("____"); tldt.test6(); } //1.LocalDate、LocalTime、LocalDateTime public void test1() { //1、输出当前时间 LocalDateTime localDateTime = LocalDateTime.now(); System.out.println(localDateTime); //2.自己指定时间 LocalDateTime localDateTime1 = LocalDateTime.of(2017, 7, 21, 21, 23, 12); System.out.println(localDateTime1); //3.给当前时间+2年或者-2年 LocalDateTime localDateTime2 = localDateTime.plusYears(2); LocalDateTime localDateTime3 = localDateTime.minusYears(2); System.out.println(localDateTime2); System.out.println(localDateTime3); //4.获得当前时间对象中的年月日，时分秒等待信息 System.out.println(localDateTime.getYear()); System.out.println(localDateTime.getMonthValue()); System.out.println(localDateTime.getDayOfMonth()); System.out.println(localDateTime.getHour()); System.out.println(localDateTime.getMonthValue()); System.out.println(localDateTime.getSecond()); } //2.Instant : 时间戳（以Unix元年： 1970.1.1 00:00:00到某个时间的毫秒值） public void test2() { //以UTC时间为基础的 Instant now = Instant.now(); System.out.println(now); //带偏移量的UTC时间 OffsetDateTime offsetDateTime = now.atOffset(ZoneOffset.ofHours(8)); System.out.println(offsetDateTime); //转换为毫秒值 System.out.println(now.toEpochMilli()); //在1970.1.1 00:00:00后面设置过去的时间 Instant instant = Instant.ofEpochSecond(60); System.out.println(instant); } /**3. * Duration : 计算两个时间的间隔 * Period : 计算两个日期之间的间隔 */ public void test3() throws InterruptedException { //查看两个时间之间的间隔 Instant ins1 = Instant.now(); Thread.sleep(1000); Instant ins2 = Instant.now(); Duration between = Duration.between(ins1, ins2); System.out.println(between.toMillis()); LocalDateTime ldt1 = LocalDateTime.now(); Thread.sleep(1000); LocalDateTime ldt2 = LocalDateTime.now(); Duration between1 = Duration.between(ldt1, ldt2); System.out.println(between1.toMillis()); //查看两个日期之间的间隔 LocalDate localDate = LocalDate.of(2014, 12, 21); LocalDate localDate1 = LocalDate.now(); Period period = Period.between(localDate, localDate1); System.out.println(period.getYears()); System.out.println(period.getMonths()); System.out.println(period.getDays()); } //4.TemporalAdjuster : 时间矫正器 public void test4(){ LocalDateTime ldt = LocalDateTime.now(); System.out.println(ldt); LocalDateTime ldt1= ldt.withDayOfMonth(10); System.out.println(ldt1); LocalDateTime ldt2 = ldt.with(TemporalAdjusters.firstDayOfMonth()); System.out.println(ldt2); //自定义下一个工作日 LocalDateTime ldt5 = ldt.with((l) -> { LocalDateTime ldt4 = (LocalDateTime) l; DayOfWeek ldt3 = ldt4.getDayOfWeek(); if (ldt3.equals(DayOfWeek.FRIDAY)){ return ldt4.plusDays(3); }else if(ldt3.equals(DayOfWeek.SATURDAY)){ return ldt4.plusDays(2); }else{ return ldt4.plusDays(1); } }); System.out.println(ldt5); } //5.DateTimeFormatter : 格式化时间或者日期 public void test5() { DateTimeFormatter dtf = DateTimeFormatter.ISO_DATE; LocalDateTime ldt = LocalDateTime.now(); String format = ldt.format(dtf); System.out.println(format); //自定义时间格式 DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss"); String format1 = ldt.format(dateTimeFormatter); System.out.println(format1); //将转换后的时间转换为原格式 LocalDateTime parse = ldt.parse(format1, dateTimeFormatter); System.out.println(parse); } //ZonedDate、 ZonedTime 、ZonedDateTime public void test6(){ //获取所有的时区 //Set<String> availableZoneIds = ZoneId.getAvailableZoneIds(); //自己指定时区 LocalDateTime now = LocalDateTime.now(); ZonedDateTime zonedDateTime = now.atZone(ZoneId.of("Europe/Tallinn")); System.out.println(zonedDateTime); } }不同看视频：https://www.bilibili.com/video/BV1xb411w7jM?p=17
