Java中常用的获取从当前月开始的前第i个月、取结束时间与开始时间相差多少个月份等的方法

@RunWith(SpringRunner.class)
@SpringBootTest
public class DateTest {
@Test
public void test(){
DateFormat dfs = new SimpleDateFormat("yyyy-MM");
String date1 = dfs.format(new Date(Long.valueOf("1546327530000")));
String date2 = dfs.format(new Date(Long.valueOf("1559373930000")));
// getLastMonths(1);
// getDifference(date1,date2);
// getMouths(new Date(),1);

    getEveryDay(new Date(),7L);
}

/**
 * 获取从当前月开始的前第i个月
 * @param i
 * @return
 */
public String getLastMonths(int i) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
    Calendar c = Calendar.getInstance();
    c.setTime(new Date());
    c.add(Calendar.MONTH, -i);
    Date m = c.getTime();
    System.out.println(sdf.format(m));
    return sdf.format(m);
}

/**
 * 获取结束时间与开始时间相差多少个月份
 * @param start
 * @param end
 * @return
 */
public int getDifference(String start, String end) {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
    String str1 = start.substring(0, 7);
    String str2 = end.substring(0, 7);
    Calendar bef = Calendar.getInstance();
    Calendar aft = Calendar.getInstance();
    try {
        bef.setTime(sdf.parse(str1));
        aft.setTime(sdf.parse(str2));
    } catch (ParseException e) {
        e.printStackTrace();
    }
    int result = aft.get(Calendar.MONTH) - bef.get(Calendar.MONTH);
    int month = (aft.get(Calendar.YEAR) - bef.get(Calendar.YEAR)) * 12;
    System.out.println(Math.abs(month + result));
    return Math.abs(month + result);
}

/**
 * 获取某个月份在i个月之前的月份
 * @param date
 * @param i
 * @return
 */

public String getMouths(Date date,int i){
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM");
    Calendar c = Calendar.getInstance();
    c.setTime(date);
    c.add(Calendar.MONTH, Integer.valueOf("-"+i));
    Date m = c.getTime();
    String mon = format.format(m);
    System.out.println("过去一个月："+mon);
    return mon;
}

/**
 * 计算两个时间点相差多少天、多少小时、多少分钟
 * @param date1
 * @param date2
 * @return
 * @throws ParseException
 */
public Long getDay(Date date1,Date date2) throws ParseException {
    long nd = 1000 * 24 * 60 * 60;//每天毫秒数
    long nh = 1000 * 60 * 60;//每小时毫秒数
    long nm = 1000 * 60;//每分钟毫秒数
    long diff = date2.getTime() - date1.getTime(); // 获得两个时间的毫秒时间差异
    long day = diff / nd;   // 计算差多少天
    long hour = diff % nd / nh; // 计算差多少小时
    long min = diff % nd % nh / nm;  // 计算差多少分钟
    return  day;
}

/**
 *  计算某个时间点在i天之前的时间点
 *
 * @param date
 * @param i
 * @return
 */
public String getEveryDay(Date date,Long i){
    SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
    Calendar c = Calendar.getInstance();
    c.setTime(date);
    c.add(Calendar.DATE, Integer.valueOf("-"+i));
    Date d = c.getTime();
    String day = format.format(d);
    System.out.println("过去七天："+day);
    return day;
}

}