JAVA得到某个日期的前几天或者后几天

SimpleDateFormat sdf=new SimpleDateFormat( "yyyyMMdd ");

String str= "20011230 ";

Date dt=sdf.parse(str,new ParsePosition(0));

Calendar rightNow = Calendar.getInstance();

rightNow.setTime(dt);

rightNow.add(Calendar.DATE,2);//你要加减的日期

Date dt1=rightNow.getTime();

String reStr=sdf.format(dt1, " ",new FieldPosition(0));

System.out.println(reStr);