计算时间差（天、时、分）

                diff = calendar.getTime().getTime() - new Date().getTime();
                days = diff / (24 * 60 * 60 * 1000);
                hours = (diff / (60 * 60 * 1000) - days * 24);
                mins = ((diff / (60 * 1000)) - days * 24 * 60 - hours * 60);