java根据生日计算当前年龄，精确到月

public static String getAgeDetail(String date){
    //如果有空格
    int index = date.indexOf(" ");
    if (index != -1){
        date = date.substring(0 , index);
    }
    String[] data = date.split("-");

    Calendar birthday =new GregorianCalendar(Integer.valueOf(data[0]), Integer.valueOf(data[1]), Integer.valueOf(data[2]));
    Calendar now = Calendar.getInstance();

    int day = now.get(Calendar.DAY_OF_MONTH) - birthday.get(Calendar.DAY_OF_MONTH);
    //月份从0开始计算，所以需要+1
    int month = now.get(Calendar.MONTH) +1 - birthday.get(Calendar.MONTH);
    int year = now.get(Calendar.YEAR) - birthday.get(Calendar.YEAR);

    //按照减法原理，先day相减，不够向month借；然后month相减，不够向year借；最后year相减。
    if (day <0) {
        month -=1;
        now.add(Calendar.MONTH, -1);//得到上一个月，用来得到上个月的天数。
        day = day + now.getActualMaximum(Calendar.DAY_OF_MONTH);
    }

    if (month <0) {

        month = (month +12) %12;

        year--;

    }

    StringBuffer tag =new StringBuffer();
    if (year >0) {

        tag.append(year +".");

    }
    if (month >0) {

        tag.append(month);

    }
    if (year ==0 && month ==0 && day ==0) {

        tag.append("今日出生");

    }
    return String.valueOf(tag);
}