java 日期 前面几天

public static String getTodayTime() {
		String strTodayTime = "" ; //19880214这样形式
		Date now = new Date() ;
		SimpleDateFormat f= new SimpleDateFormat("yyyy-MM-dd");
		strTodayTime = f.format(now) ;  
		return  strTodayTime ;

	}
	
	/**
	 * 得到当前日期的前的第beforData天的日期
	 * @param beforData
	 * @return
	 */
	public static String  getBeforeDaysTime(int beforData) {
		
		GregorianCalendar calendar = new GregorianCalendar();
		SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
		calendar.set(Calendar.DATE, calendar.get(Calendar.DATE) - beforData);
		Date date = calendar.getTime();
		return df.format(date);
	}