如何计算两个时间相差多少周年

public static Calendar getCalendarFromString(String dateStr, String dateFormatType) {
SimpleDateFormat sdf = new SimpleDateFormat(dateFormatType);
Calendar calendar = null;
try {
Date date = sdf.parse(dateStr);
calendar = Calendar.getInstance();
calendar.setTime(date);
} catch (ParseException e) {
e.printStackTrace();
}
return calendar;
}

/**
* 获取年份间隔，匹配到日，可以进一步扩展到时分秒
*
* @param startDate 开始时间
* @param endDate   结束事件
* @return 间隔年份
*/
public static int getYearSpace(String startDate, String endDate) {
String dateType = "yyyy-MM-dd ";
Calendar calendar1 = DateUtil.getCalendarFromString(startDate, dateType);
Calendar calendar2 = DateUtil.getCalendarFromString(endDate, dateType);
if (calendar1 == null || calendar2 == null) {
return 0;
}
if (calendar1.getTimeInMillis() > calendar2.getTimeInMillis()) {
Calendar calendar = calendar1;//修正开始时间大于结束时间
calendar1 = calendar2;
calendar2 = calendar;
}
int year1 = calendar1.get(Calendar.YEAR);
int month1 = calendar1.get(Calendar.MONTH) + 1;
int date1 = calendar1.get(Calendar.DATE);
int year2 = calendar2.get(Calendar.YEAR);
int month2 = calendar2.get(Calendar.MONTH) + 1;
int date2 = calendar2.get(Calendar.DATE);
int years = year2 - year1;
if (year1 != year2) {
if (month1 != month2) {
if (month1 > month2) {
years = years - 1;//修正如：2016-8到2017-4    未满一年
}
} else {
if (date1 != date2) {
if (date1 > date2) {
years = years - 1; //修正如：2016-8-18到2017-8-10  未满一年
}
}
}
}
return years;
}