java8新特性LocalDate、LocalTime、LocalDateTime的学习

以前操作时间都是使用SimpleDateFormat类改变Date的时间格式，使用Calendar类操作时间。但是SimpleDateFormat是线程不安全的，源码如下：

 private StringBuffer format(Date date, StringBuffer toAppendTo,
                                FieldDelegate delegate) {
        // Convert input date to time field list
        calendar.setTime(date);
 
        boolean useDateFormatSymbols = useDateFormatSymbols();
 
        for (int i = 0; i < compiledPattern.length; ) {
            int tag = compiledPattern[i] >>> 8;
            int count = compiledPattern[i++] & 0xff;
            if (count == 255) {
                count = compiledPattern[i++] << 16;
                count |= compiledPattern[i++];
            }
 
            switch (tag) {
            case TAG_QUOTE_ASCII_CHAR:
                toAppendTo.append((char)count);
                break;
 
            case TAG_QUOTE_CHARS:
                toAppendTo.append(compiledPattern, i, count);
                i += count;
                break;
 
            default:
                subFormat(tag, count, delegate, toAppendTo, useDateFormatSymbols);
                break;
            }
        }
        return toAppendTo;
    }

　　

calendar是共享变量，并且这个共享变量没有做线程安全控制。当多个线程同时使用相同的SimpleDateFormat对象调用format方法时，多个线程会同时调用calendar.setTime方法，可能一个线程刚设置好time值另外的一个线程马上把设置的time值给修改了导致返回的格式化时间可能是错误的。

所以JAVA8推出了LocalDate、LocalTime、LocalDateTime是线程安全、简易、高可靠的时间包。源码如下

1. LocalDate  获取年月日

    　　@Test
       public void localDataTest(){
           //创建LocalDate获取当前年月日
           LocalDate now = LocalDate.now();
           System.out.println("当前时间：" + now);
           //构造指定的年月日
           LocalDate localDate = LocalDate.of(2020, 11, 24);
           System.out.println("当前指定时间：" + localDate);
           int year = now.getYear();
           System.out.println("当前年year：" + year);
           int year1 = now.get(ChronoField.YEAR);
           System.out.println("当前年year1：" + year1);
           Month month = now.getMonth();
           System.out.println("当前月month：" + month);
           int month1 = now.get(ChronoField.MONTH_OF_YEAR);
           System.out.println("当前月month1：" + month1);
           int day = now.getDayOfMonth();
           System.out.println("当前天day：" + day);
           int day1 = now.get(ChronoField.DAY_OF_MONTH);
           System.out.println("当前天day1：" + day1);
           DayOfWeek dayOfWeek = now.getDayOfWeek();
           System.out.println("当前星期几dayOfWeek：" + dayOfWeek);
           int dayOfWeek1 = now.get(ChronoField.DAY_OF_WEEK);
           System.out.println("当前星期几dayOfWeek1：" + dayOfWeek1);
       }

   　　

2. LocalTime   获取时分秒

   　　@Test
       public void localTimeTest(){
           //创建LocalTime获取当前时分秒
           LocalTime now = LocalTime.now();
           System.out.println("当前时间：" + now);
           LocalTime localTime = LocalTime.of(13, 51, 10);
           System.out.println("指定时间：" + localTime);
           int hour = now.getHour();
           System.out.println("当前小时数hour："+ hour);
           int hour1 = now.get(ChronoField.HOUR_OF_DAY);
           System.out.println("当前小时数hour1："+ hour1);
           int minute = now.getMinute();
           System.out.println("当前分钟数minute："+ minute);
           int minute1 = now.get(ChronoField.MINUTE_OF_DAY);
           System.out.println("当前分钟数minute1："+ minute1);
           int second = now.getSecond();
           System.out.println("当前秒数second："+ second);
           int second1 = now.get(ChronoField.SECOND_OF_MINUTE);
           System.out.println("当前秒数second1："+ second1);
       }

   　　

3. LocalDateTime   获取年月日时分秒，相当于LocalDate+LocalTime，可与LocalDate、LocalTime相互转换

       @Test
       public void localDataTimeTest(){
   　　　　 //创建localDateTime获取当前年月日时分秒
           LocalDateTime localDateTime = LocalDateTime.now();
           System.out.println("当前时间：" + localDateTime);
           LocalDateTime localDateTime1 = LocalDateTime.of(2020, Month.SEPTEMBER, 10, 14, 46, 56);
           System.out.println("指定时间：" + localDateTime1);
           LocalDateTime of = LocalDateTime.of(LocalDate.now(), LocalTime.now());
           System.out.println("当前时间1：" + of);
           LocalDateTime localDateTime2 = LocalDate.now().atTime(LocalTime.now());
           System.out.println("当前时间2：" + localDateTime2);
           LocalDateTime localDateTime3 = LocalTime.now().atDate(LocalDate.now());
           System.out.println("当前时间3：" + localDateTime3);
           LocalDate localDate = localDateTime.toLocalDate();
           System.out.println("当前年月日：" + localDate);
           LocalTime localTime = localDateTime.toLocalTime();
           System.out.println("当前时分秒：" + localTime);
    
       }

   　　

4. Period  时间长度类   Period表示以年、月、日衡量的时长，通过Period增加、减少年月日

       @Test
       public void periodTest(){
           //创建localDateTime获取当前年月日时分秒
           LocalDateTime localDateTime = LocalDateTime.now();
           //创建Period对象，设置一年
           Period period = Period.ofYears(1);
           //增加一年
           LocalDate localDate = localDateTime.toLocalDate().plus(period);
           System.out.println("增加一年后的时间：" + localDate);
           Period period1 = Period.ofYears(-1);
           //减少一年
           LocalDate localDate1 = localDateTime.toLocalDate().plus(period1);
           System.out.println("减少一年后的时间：" + localDate1);
           //创建Period对象，设置一月
           Period period2 = Period.ofMonths(1);
           //增加一个月
           LocalDate localDate2 = localDateTime.toLocalDate().plus(period2);
           System.out.println("增加一个月后的时间：" + localDate2);
           //创建Period对象，设置一周
           Period period3 = Period.ofWeeks(1);
           //增加一周
           LocalDate localDate3 = localDateTime.toLocalDate().plus(period3);
           System.out.println("增加一周后的时间：" + localDate3);
           //创建Period对象，设置一天
           Period period4 = Period.ofDays(1);
           //增加一天
           LocalDate localDate4 = localDateTime.toLocalDate().plus(period4);
           System.out.println("增加一天后的时间：" + localDate4);
       }

   　　

5. Duration  时间长度类   Duration表示以时、分、秒衡量的时长，通过Duration增加、减少时分秒

       @Test
       public void durationTest(){
           //创建localDateTime获取当前时间时分秒
           LocalDateTime localDateTime = LocalDateTime.now();
           //创建Duration对象，设置1天
           Duration duration = Duration.ofDays(1);
           //增加一天
           LocalTime localTime = localDateTime.toLocalTime().plus(duration);
           System.out.println("增加一天后时间：" + localTime);
           //创建Duration对象，设置一小时
           Duration duration1 = Duration.ofHours(-1);
           //减少一天
           LocalTime localTime1 = localDateTime.toLocalTime().plus(duration1);
           System.out.println("增加一天后时间：" + localTime1);
           //创建Duration对象，设置一小时
           Duration duration2 = Duration.ofHours(1);
           //增加一小时
           LocalTime localTime2 = localDateTime.toLocalTime().plus(duration2);
           System.out.println("增加一小时后时间：" + localTime2);
           //创建Duration对象，设置一分钟
           Duration duration3 = Duration.ofMinutes(1);
           //增加一分钟
           LocalTime localTime3 = localDateTime.toLocalTime().plus(duration3);
           System.out.println("增加一分钟后时间：" + localTime3);
           //创建Duration对象，设置十秒钟
           Duration duration4 = Duration.ofSeconds(10);
           //增加十秒钟
           LocalTime localTime4 = localDateTime.toLocalTime().plus(duration4);
           System.out.println("增加十秒钟后时间：" + localTime4);
           //创建Duration对象，设置一百毫秒
           Duration duration5 = Duration.ofMillis(100);
           //增加一百毫秒
           LocalTime localTime5 = localDateTime.toLocalTime().plus(duration5);
           System.out.println("增加一百毫秒后时间：" + localTime5);
       }

   　　

6. ZonedDateTime   时区处理类   可以设置时区

       @Test
       public void zonedDateTimeTest(){
           ZoneId zoneId = ZoneId.of("UTC+1");
           //设置指定时间、时区
           ZonedDateTime zonedDateTime = ZonedDateTime.of(2020, 11, 24, 15, 29, 53, 1026, zoneId);
           //获取今天是今年第几天
           int dayOfYear = zonedDateTime.getDayOfYear();
           System.out.println("今天是今年第"+dayOfYear+"天");
           //获取今天是这月第几天
           int dayOfMonth = zonedDateTime.getDayOfMonth();
           System.out.println("今天是这月第"+dayOfMonth+"天");
           //获取今天是这周第几天
           int dayOfWeek = zonedDateTime.getDayOfWeek().get(ChronoField.DAY_OF_WEEK);
           System.out.println("今天是这周第"+dayOfWeek+"天");
           //增加一年
           ZonedDateTime zonedDateTime1 = zonedDateTime.plusYears(1);
           System.out.println("增加一年后的时间："+zonedDateTime1);
           //减少一年
           ZonedDateTime zonedDateTime2 = zonedDateTime.minusYears(1);
           System.out.println("减少一年后的时间："+zonedDateTime2);
    
       }