public static String before30Day(String time) {
        DateFormat dateFromat = new SimpleDateFormat(TIME_STAMP_STANDARD);
        try {
            Date parse = dateFromat.parse(time);

            Calendar cal = Calendar.getInstance();// get a calendar by using default timezone and language
            cal.setTime(parse);
            cal.add(Calendar.DAY_OF_MONTH, -30);
            Date date = cal.getTime();
            return dateFromat.format(date);

        } catch (ParseException e) {
            e.printStackTrace();
        }
        return null;
    }

 

 

 

 

    public static void main(String[] args) {
        //获取东八区时间
            Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT+08:00"));    
            //获取年
             int year = c.get(Calendar.YEAR);   
             //获取月份，会少一天。所以+1
             int month = c.get(Calendar.MONTH) + 1;   
             //获取当前天数
             int day = c.get(Calendar.DAY_OF_MONTH);  
             
                c.add(Calendar.YEAR,5);
                c.add(Calendar.DATE, +10);
             //获取当前小时
             int h= c.get(Calendar.HOUR_OF_DAY);       
             //获取当前分钟
             int m = c.get(Calendar.MINUTE);          
             //获取当前秒
             int se = c.get(Calendar.SECOND);   
             
             SimpleDateFormat s=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
             //格式化时间格式
             String Now = s.format(c.getTime());  
             //获得当前日期     format（Obj）：格式化一个对象以生成一个字符串。
             System.out.println("当前时间:" + year + "-" + month + "-"+ day + " "+h+":" + m +":" + se);
             System.out.println("当前日期Now:" + Now);
    }