java string时间类型天数运算

 调用addDay即可

day:2019-03-01  也可精确到毫秒

n：增加的天数

    //实现天数的增加
    public static String addDay(String day,Integer n){
        String f = "yyyy-MM-dd HH:mm:ss";
        SimpleDateFormat sdf = new SimpleDateFormat();
        Date d1 = conversionToDate(day,f);
        Calendar c = Calendar.getInstance();
        c.setTime(d1);
        c.add(Calendar.DAY_OF_MONTH, n);//利用Calendar 实现 Date日期+1天
        d1 = c.getTime();
        return sdf.format(d1);
    }

    //格式化时间
    public static Date conversionToDate(String date, String format){
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        Date d = null;
        try {
            d = sdf.parse(date);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return d;
    }