src/org/nutz/lang/Times.java
public static Date nextDay(Date date, int day) {
        Calendar cal = Calendar.getInstance();
        if (date != null) {
            cal.setTime(date);
        }
        cal.add(Calendar.DAY_OF_YEAR, day);
        return cal.getTime();
    }
public static Date nextDay(Date date, int day) {
        Calendar cal = Calendar.getInstance();
        if (date != null) {
            cal.setTime(date);
        }
        cal.add(Calendar.DAY_OF_YEAR, day);
        return cal.getTime();
    }
取得指定日期过 day 天后的日期 (当 day 为负数表示指日期之前);

@param date
日期 为null时表示当天
@param day
相加(相减)的月数