SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        long currentTime =System.currentTimeMillis();
        //从对象中拿到时间
        long createTime = df.parse("2021-02-19 17:50:50").getTime();
        long diff=(currentTime-createTime)/1000/60;
        System.out.println("当前系统时间为："+currentTime+"下单时间为："+createTime+"两个时间差为："+diff);