java计算今天起后7天时间 +昨天八点+今天前7天的日期

/**
 * 今天起 近7天日期 后七天
 * @param days=6
 * @return
 */
public static List<String> getDaysBetwwen(int days){ //最近几天日期
    List<String> dayss = new ArrayList<>();
    Calendar start = Calendar.getInstance();
    start.setTime(new Date());
    Long startTIme = start.getTimeInMillis();
    Calendar end = Calendar.getInstance();
    end.setTime(getDateAdd(days));
    Long endTime = end.getTimeInMillis();
    Long oneDay = 1000 * 60 * 60 * 24l;
    Long time = startTIme;
    while (time <= endTime) {
        Date d = new Date(time);
        DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println(df.format(d));
        dayss.add(df.format(d));
        time += oneDay;
    }
    return dayss;
}

private static  Date getDateAdd(int days){
    SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
    Calendar c = Calendar.getInstance();
    c.add(Calendar.DAY_OF_MONTH, +days);
 }

/**
 * 昨天八点
 * @return
 */
public static String getYesterday(){
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");//日期格式
    Calendar cale = Calendar.getInstance();  // 取当前日期。
    Calendar calendar = Calendar.getInstance();
         calendar.set(Calendar.HOUR_OF_DAY,8);
        calendar.set(Calendar.MINUTE,0);
        calendar.set(Calendar.SECOND,0);
        calendar.set(Calendar.MILLISECOND,0);
        calendar.add(Calendar.DAY_OF_YEAR,-1);
        Date date = calendar.getTime();
    return format.format(date);
}

/**
 * 今天起 近7天日期 后7天
 * @param days
 * @return
 */
public static List<String> getDaysBetwwen(int days){ //最近几天日期
    List<String> dayss = new ArrayList<>();
    Calendar start = Calendar.getInstance();
    start.setTime(getDateAdd(days));
    Long startTIme = start.getTimeInMillis();
    Calendar end = Calendar.getInstance();
    end.setTime(new Date());
    Long endTime = end.getTimeInMillis();
    Long oneDay = 1000 * 60 * 60 * 24l;
    Long time = startTIme;
    while (time <= endTime) {
        Date d = new Date(time);
        DateFormat df = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println(df.format(d));
        dayss.add(df.format(d));
        time += oneDay;
    }
    return dayss;
}

private static  Date getDateAdd(int days){
    SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
    Calendar c = Calendar.getInstance();
    c.add(Calendar.DAY_OF_MONTH, -days);
    return c.getTime();
}