Date starttime=new Date();
Calendar cal = Calendar.getInstance();
cal.setTime(starttime);
cal.set(Calendar.DATE, cal.get(Calendar.DATE) - 2);
starttime= cal.getTime();
JAVA Calendar 日期加减,布布扣,bubuko.com
原文：http://www.cnblogs.com/jsnhj/p/3889712.html