public static void main(String[] args) {
        LocalDateTime now=LocalDateTime.now();
        //年月日时分秒毫秒
        System.out.println(now.format(DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS")));
        //年月日时分秒毫秒
        System.out.println(now.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss:SSS")));
        //生成年月日
        System.out.println(now.format(DateTimeFormatter.ISO_DATE));
        System.out.println(now.format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
        //年月日时分秒
        System.out.println(now.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
        
    }

20191531191523234  //一般用于生成订单流水号
2019-08-31 19:15:23:234
2019-08-31
2019-08-31
2019-08-31 19:15:23