关于Java8新特性总结一文:，使用YYYY显示年份时，会显示当前时间所在周的年份，在跨年周会有问题。一般情况下都使用yyyy，来显示准确的年份。 #1157

        LocalDateTime rightNow=LocalDateTime.now();
        String date=DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(rightNow);
        System.out.println(date);//2019-03-12T16:26:48.29
        DateTimeFormatter formatter=DateTimeFormatter.ofPattern("YYYY-MM-dd HH:mm:ss");
        System.out.println(formatter.format(rightNow));//2019-03-12 16:26:48

        LocalDateTime rightNow = LocalDateTime.of(2020, 12, 31, 12, 0, 0);
        String date= DateTimeFormatter.ISO_LOCAL_DATE_TIME.format(rightNow);
        // 2020-12-31T12:00:00
        System.out.println(date);
        DateTimeFormatter formatterOfYYYY = DateTimeFormatter.ofPattern("YYYY-MM-dd HH:mm:ss");
        // 2021-12-31 12:00:00
        System.out.println(formatterOfYYYY.format(rightNow));
        
        DateTimeFormatter formatterOfYyyy = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        // 2020-12-31 12:00:00
        System.out.println(formatterOfYyyy.format(rightNow));