如果你不想使用JodaTime或类似的，最好的解决方案可能是:

final static long MILLIS_PER_DAY = 24 * 3600 * 1000;
long msDiff= date1.getTime() - date2.getTime();
long daysDiff = Math.round(msDiff / ((double)MILLIS_PER_DAY));

每天的毫秒数并不总是相同的(因为日光节约时间和闰秒)，但它非常接近，至少由于日光节约时间的偏差在较长时间内抵消了。因此，除法和舍入将给出正确的结果(至少只要所使用的本地日历不包含DST和闰秒以外的奇怪时间跳转)。

请注意，这仍然假设date1和date2被设置为一天中的同一时间。对于一天中的不同时间，你首先必须定义“日期差异”的含义，正如乔恩·斯基特指出的那样。

最好的办法是

(Date1-Date2)/86 400 000 

这个数字是一天的毫秒数。

一个日期和另一个日期的差异以毫秒为单位。

在双变量中收集答案。

Since dates can contain hours and minutes, final result will be rounded down, which will result in incorrect value. For example, you calculate difference between today at 22:00 p.m and day after tomorrow 00:00 a.m, so the final result will be 1, because in reality it was 1.08 or smth difference, then it gets rounded down when calling TimeUnit.MILLISECONDS.toDays(..). That's why you need to take that in account, so in my solution I subtract the remainder of milliseconds from milliseconds in a day. Additionally, if you want to count the end date, you need to +1 it.

import java.util.Date;
import java.util.concurrent.TimeUnit;

public static long getDaysBetween(Date date1, Date date2, boolean includeEndDate) {
        long millisInDay = 60 * 60 * 24 * 1000;
        long difference = Math.abs(date1.getTime() - date2.getTime());
        long add = millisInDay - (difference % millisInDay);//is used to calculate true number of days, because by default hours, minutes are also counted

        return TimeUnit.MILLISECONDS.toDays(difference + add) + (includeEndDate ? 1 : 0);
    }

测试:

Date date1 = new Date(121, Calendar.NOVEMBER, 27); //2021 Nov 27
Date date2 = new Date(121, Calendar.DECEMBER, 29); //2021 Dec 29
System.out.println( getDaysBetween(date1, date2, false) ); //32 days difference
System.out.println( getDaysBetween(date1, date2, true) ); //33 days difference

以毫秒为单位减去日期是可行的(如另一篇文章所述)，但在清除日期的时间部分时，你必须使用HOUR_OF_DAY而不是HOUR:

public static final long MSPERDAY = 60 * 60 * 24 * 1000;
...
final Calendar dateStartCal = Calendar.getInstance();
dateStartCal.setTime(dateStart);
dateStartCal.set(Calendar.HOUR_OF_DAY, 0); // Crucial.
dateStartCal.set(Calendar.MINUTE, 0);
dateStartCal.set(Calendar.SECOND, 0);
dateStartCal.set(Calendar.MILLISECOND, 0);
final Calendar dateEndCal = Calendar.getInstance();
dateEndCal.setTime(dateEnd);
dateEndCal.set(Calendar.HOUR_OF_DAY, 0); // Crucial.
dateEndCal.set(Calendar.MINUTE, 0);
dateEndCal.set(Calendar.SECOND, 0);
dateEndCal.set(Calendar.MILLISECOND, 0);
final long dateDifferenceInDays = ( dateStartCal.getTimeInMillis()
                                  - dateEndCal.getTimeInMillis()
                                  ) / MSPERDAY;
if (dateDifferenceInDays > 15) {
    // Do something if difference > 15 days
}

只需在两个Date对象上使用下面的方法。如果你想传递当前日期，只需传递new date()作为第二个参数，因为它是用当前时间初始化的。

public String getDateDiffString(Date dateOne, Date dateTwo)
{
    long timeOne = dateOne.getTime();
    long timeTwo = dateTwo.getTime();
    long oneDay = 1000 * 60 * 60 * 24;
    long delta = (timeTwo - timeOne) / oneDay;

    if (delta > 0) {
        return "dateTwo is " + delta + " days after dateOne";
    }
    else {
        delta *= -1;
        return "dateTwo is " + delta + " days before dateOne";
     }
}

此外，除了从天数，如果，你也想要其他参数的差异，使用下面的片段，

int year = delta / 365;
int rest = delta % 365;
int month = rest / 30;
rest = rest % 30;
int weeks = rest / 7;
int days = rest % 7;

p.s. Code完全取自SO答案。

查看示例http://www.roseindia.net/java/beginners/DateDifferent.shtml 这个例子给出了天、小时、分钟、秒和毫秒的差异:)。

import java.util.Calendar;
import java.util.Date;

public class DateDifferent {
    public static void main(String[] args) {
        Date date1 = new Date(2009, 01, 10);
        Date date2 = new Date(2009, 07, 01);
        Calendar calendar1 = Calendar.getInstance();
        Calendar calendar2 = Calendar.getInstance();
        calendar1.setTime(date1);
        calendar2.setTime(date2);
        long milliseconds1 = calendar1.getTimeInMillis();
        long milliseconds2 = calendar2.getTimeInMillis();
        long diff = milliseconds2 - milliseconds1;
        long diffSeconds = diff / 1000;
        long diffMinutes = diff / (60 * 1000);
        long diffHours = diff / (60 * 60 * 1000);
        long diffDays = diff / (24 * 60 * 60 * 1000);
        System.out.println("\nThe Date Different Example");
        System.out.println("Time in milliseconds: " + diff + " milliseconds.");
        System.out.println("Time in seconds: " + diffSeconds + " seconds.");
        System.out.println("Time in minutes: " + diffMinutes + " minutes.");
        System.out.println("Time in hours: " + diffHours + " hours.");
        System.out.println("Time in days: " + diffDays + " days.");
    }
}