看看Joda Time，它是一个改进的Java日期/时间API，应该可以很好地与Scala一起工作。

由于这里所有的答案都是正确的，但使用传统java或第三方库，如joda或类似的，我将放弃使用新java的另一种方式。Java 8及以后版本中的时间类。参见Oracle教程。

使用LocalDate和ChronoUnit:

LocalDate d1 = LocalDate.of(2017, 5, 1);
LocalDate d2 = LocalDate.of(2017, 5, 18);

long days = ChronoUnit.DAYS.between(d1, d2);
System.out.println( days );

简单的diff(不含lib)

/**
 * Get a diff between two dates
 * @param date1 the oldest date
 * @param date2 the newest date
 * @param timeUnit the unit in which you want the diff
 * @return the diff value, in the provided unit
 */
public static long getDateDiff(Date date1, Date date2, TimeUnit timeUnit) {
    long diffInMillies = date2.getTime() - date1.getTime();
    return timeUnit.convert(diffInMillies,TimeUnit.MILLISECONDS);
}

然后你可以调用:

getDateDiff(date1,date2,TimeUnit.MINUTES);

以分钟为单位获取两个日期的差值。

TimeUnit是java.util.concurrent。TimeUnit，一个从纳米到天的标准Java枚举。

人类可读的差异(不含lib)

public static Map<TimeUnit,Long> computeDiff(Date date1, Date date2) {

    long diffInMillies = date2.getTime() - date1.getTime();

    //create the list
    List<TimeUnit> units = new ArrayList<TimeUnit>(EnumSet.allOf(TimeUnit.class));
    Collections.reverse(units);

    //create the result map of TimeUnit and difference
    Map<TimeUnit,Long> result = new LinkedHashMap<TimeUnit,Long>();
    long milliesRest = diffInMillies;

    for ( TimeUnit unit : units ) {
        
        //calculate difference in millisecond 
        long diff = unit.convert(milliesRest,TimeUnit.MILLISECONDS);
        long diffInMilliesForUnit = unit.toMillis(diff);
        milliesRest = milliesRest - diffInMilliesForUnit;

        //put the result in the map
        result.put(unit,diff);
    }

    return result;
}

http://ideone.com/5dXeu6

输出类似Map:{DAYS=1, HOURS=3, MINUTES=46, SECONDS=40, MILLISECONDS=0, MICROSECONDS=0, NANOSECONDS=0}，单位是有序的。

您只需将该映射转换为用户友好的字符串。

警告

上面的代码段计算两个瞬间之间的简单差。它会在夏令时切换期间导致问题，就像这篇文章中解释的那样。这意味着如果你计算没有时间的日期之间的差异，你可能会少了一天/小时。

在我看来，日期的差异是主观的，尤其是在日子上。你可以:

计算经过24小时的时间:day+1 - day = 1 day = 24h 计算经过的时间，考虑到夏令时:天+1 -天= 1 = 24小时(但使用午夜时间和夏令时，它可以是0天和23小时) 计算日开关的数量，这意味着一天+1 1pm -一天11am = 1天，即使经过的时间只有2h(如果有夏令时则为1h:p)

我的答案是有效的，如果你的日期差异的定义天匹配第一种情况

与JodaTime

如果你正在使用JodaTime，你可以得到2个瞬间的差异(millies支持ReadableInstant)日期:

Interval interval = new Interval(oldInstant, new Instant());

但是你也可以得到本地日期/时间的差异:

// returns 4 because of the leap year of 366 days
new Period(LocalDate.now(), LocalDate.now().plusDays(365*5), PeriodType.years()).getYears() 

// this time it returns 5
new Period(LocalDate.now(), LocalDate.now().plusDays(365*5+1), PeriodType.years()).getYears() 

// And you can also use these static methods
Years.yearsBetween(LocalDate.now(), LocalDate.now().plusDays(365*5)).getYears()

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

Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();

https://www.joda.org/joda-time/faq.html#datediff

在某些地区使用毫秒方法可能会导致问题。

举个例子，03/24/2007和03/25/2007之间的差应该是1天;

然而，如果使用毫秒路径，你将得到0天，如果你在英国运行这个!

/** Manual Method - YIELDS INCORRECT RESULTS - DO NOT USE**/  
/* This method is used to find the no of days between the given dates */  
public long calculateDays(Date dateEarly, Date dateLater) {  
   return (dateLater.getTime() - dateEarly.getTime()) / (24 * 60 * 60 * 1000);  
} 

更好的实现方法是使用java.util.Calendar

/** Using Calendar - THE CORRECT WAY**/  
public static long daysBetween(Calendar startDate, Calendar endDate) {  
  Calendar date = (Calendar) startDate.clone();  
  long daysBetween = 0;  
  while (date.before(endDate)) {  
    date.add(Calendar.DAY_OF_MONTH, 1);  
    daysBetween++;  
  }  
  return daysBetween;  
}