java日期格式转换

public class LoopRead { 
    public static void main(String[] args) { 
        loopRead();
    }
    public static void loopRead(){ 
        long timeMillis = System.currentTimeMillis();
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
        for (int i = 1; i < 30; i++) { 
            long dateTime = timeMillis - (86400000l * i);
            Date date = new Date();
            date.setTime(dateTime);
            String dateString = dateFormat.format(date);
            System.out.println(dateString);
        }
    }
}