Java计算两个字符串日期之间的天数差

调用方法：

public static void main(String[] args) throws ParseException {        String a = "2017-12-01"; // 时间字符串        String b = "2017-12-31";        Long between_dayInteger = between_days(a, b);        System.out.println(between_dayInteger);    }

控制台输出：

封装方法：

public static Long between_days(String a, String b) {        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");// 自定义时间格式        Calendar calendar_a = Calendar.getInstance();// 获取日历对象        Calendar calendar_b = Calendar.getInstance();        Date date_a = null;        Date date_b = null;        try {            date_a = simpleDateFormat.parse(a);//字符串转Date            date_b = simpleDateFormat.parse(b);            calendar_a.setTime(date_a);// 设置日历            calendar_b.setTime(date_b);        } catch (ParseException e) {            e.printStackTrace();//格式化异常        }        long time_a = calendar_a.getTimeInMillis();        long time_b = calendar_b.getTimeInMillis();        long between_days = (time_b - time_a) / (1000 * 3600 * 24);//计算相差天数        return between_days;    }