java8新时间与日期

一：解决传统时间格式化线程安全问题

传统时间格式化使用SimpleDateFormat类，但SimpleDateFormat不是一个线程安全的类，在多线程中会报错

    public static void main(String[] args) throws Exception{
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
        Callable<Date> task = () -> sdf.parse("20190813");
        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());
        }
    }

执行这段代码会发现报 java.lang.NumberFormatException: multiple points异常。

在java8中使用DateTimeFormatter就可以解决这个问题

    public static void main(String[] args) throws Exception{
        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyyMMdd");
        Callable<LocalDate> task = () -> LocalDate.parse("20190813", df);
        ExecutorService pool = Executors.newFixedThreadPool(10);
        
        List<Future<LocalDate>> results = new ArrayList<>();
        for(int i = 0; i < 10; i++) {
            results.add(pool.submit(task));
        }
        
        for(Future<LocalDate> future : results) {
            System.out.println(future.get());
        }
    }

二：新时间与新日期类型

1.LocalDate、LocalTime、LocalDateTime

    public static void newDateTime() {
        //获取当前时间
        LocalDateTime ldt = LocalDateTime.now();
        System.out.println(ldt);
        
        //获取指定年月日时分秒的时间
        LocalDateTime ldt2 = LocalDateTime.of(2019, 9, 13, 18, 8, 4);
        System.out.println(ldt2);
        
        //增加/减少年份，增加/减少月、日、周、时、分、秒同理
        LocalDateTime ldt3 = ldt.plusYears(2);
        System.out.println(ldt3);
        LocalDateTime ldt4 = ldt.minusYears(2);
        System.out.println(ldt4);
        
        //获取年、月
        System.out.println(ldt.getYear());
        System.out.println(ldt.getMonthValue());
        
    }

2.Instant：时间戳

    public static void newInstant() {
        //Instant.now()默认获取UTC时区，UTC时区与北京时间有8小时偏差
        Instant ins1 = Instant.now();
        System.out.println(ins1);
        
        //设置与UTC时区的偏移
        OffsetDateTime odt = ins1.atOffset(ZoneOffset.ofHours(8));
        System.out.println(odt);
        
        //获取毫秒级时间戳
        System.out.println(ins1.toEpochMilli());
        
    }

3.Duration：计算两个时间之间的间隔；Period：计算两个日期之间的间隔

    public static void calculateInterval() throws Exception{
        Instant ins1 = Instant.now();
        Thread.sleep(1000);
        Instant ins2 = Instant.now();
        //计算两个时间之间的间隔
        Duration duration = Duration.between(ins1, ins2);
        System.out.println(duration.toMillis());
        
        
        LocalDate ld1 = LocalDate.of(2015, 3, 22);
        LocalDate ld2 = LocalDate.now();
        //计算两个日期之间的间隔
        Period period = Period.between(ld1, ld2);
        System.out.println(period);
        //获取日期间隔的年、月、日
        System.out.println(period.getYears());
        System.out.println(period.getMonths());
        System.out.println(period.getDays());
        
    }

4. TemporalAdjuster：时间校正器

    public static void demoTemporalAdjuster() {
        LocalDateTime ldt1 = LocalDateTime.now();
        System.out.println(ldt1);
        
        //获取当月的第十天的日期
        LocalDateTime ldt2 = ldt1.withDayOfMonth(10);
        System.out.println(ldt2);
        
        //获取下一个周末的日期
        LocalDateTime ldt3 = ldt1.with(TemporalAdjusters.next(DayOfWeek.SUNDAY));
        System.out.println(ldt3);
        
        //自定义获取下一个工作日的日期
        LocalDateTime ldt5 = ldt1.with((l) -> {
            LocalDateTime ldt4 = (LocalDateTime) l;
            
            DayOfWeek dayOfWeek = ldt4.getDayOfWeek();
            
            if(dayOfWeek.equals(DayOfWeek.FRIDAY)) {
                return ldt4.plusDays(3);
            } else if(dayOfWeek.equals(DayOfWeek.SATURDAY)) {
                return ldt4.plusDays(2);
            } else {
                return ldt4.plusDays(1);
            }
        });
        System.out.println(ldt5);
    }

5.格式化时间：DateTimeFormatter

    public static void demoDateTimeFormatter() {
        LocalDateTime now = LocalDateTime.now();
        
        //定义日期转换模式
        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss");
        
        //日期格式化
        String formatDateStr = df.format(now);
        System.out.println(formatDateStr);
        
        //转换日期
        LocalDateTime newDate = LocalDateTime.parse(formatDateStr, df);
        System.out.println(newDate);
    }