SimpleDateFormat sdf  = new SimpleDateFormat("yyyy-MM-dd");  
        String maxDateStr = "2017-02-08";  
        String minDateStr = "";  
        Calendar calc =Calendar.getInstance();  
        try {  
            calc.setTime(sdf.parse(maxDateStr));  
            calc.add(calc.DATE, -30);  
            Date minDate = calc.getTime();  
            minDateStr = sdf.format(minDate);  
            System.out.println("minDateStr:"+minDateStr);//minDateStr:2017-01-09   正确！！！！  
        } catch (ParseException e1) {  
            // TODO Auto-generated catch block  
            e1.printStackTrace();  
        }  

转自《java,取30天前的日期》