// Create one day 00:00:00 calendar
int oneDayTimeStamp = 1523017440;
Calendar oneDayCal = Calendar.getInstance();
oneDayCal.setTimeInMillis(oneDayTimeStamp * 1000L);
oneDayCal.set(Calendar.HOUR_OF_DAY, 0);
oneDayCal.set(Calendar.MINUTE, 0);
oneDayCal.set(Calendar.SECOND, 0);
oneDayCal.set(Calendar.MILLISECOND, 0);

// Create current day 00:00:00 calendar
Calendar currentCal = Calendar.getInstance();
currentCal.set(Calendar.HOUR_OF_DAY, 0);
currentCal.set(Calendar.MINUTE, 0);
currentCal.set(Calendar.SECOND, 0);
currentCal.set(Calendar.MILLISECOND, 0);

if (oneDayCal.compareTo(currentCal) == 0) {
    // Same day (excluding time)
}

public static Date getZeroTimeDate(Date fecha) {
    Date res = fecha;
    Calendar calendar = Calendar.getInstance();

    calendar.setTime( fecha );
    calendar.set(Calendar.HOUR_OF_DAY, 0);
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);
    calendar.set(Calendar.MILLISECOND, 0);

    res = calendar.getTime();

    return res;
}

Date currentDate = getZeroTimeDate(new Date());// get current date   

这是解决这个问题最简单的方法。

我也更喜欢Joda Time，但这里有一个替代方案:

long oneDay = 24 * 60 * 60 * 1000
long d1 = first.getTime() / oneDay
long d2 = second.getTime() / oneDay
d1 == d2

EDIT

我把UTC的东西放在下面，以防你需要比较UTC以外的特定时区的日期。如果你确实有这样的需求，那么我真的建议你去找Joda。

long oneDay = 24 * 60 * 60 * 1000
long hoursFromUTC = -4 * 60 * 60 * 1000 // EST with Daylight Time Savings
long d1 = (first.getTime() + hoursFromUTC) / oneDay
long d2 = (second.getTime() + hoursFromUTC) / oneDay
d1 == d2

我更倾向于直接使用Joda库而不是java.util.Date，因为Joda区分了日期和时间(参见YearMonthDay和DateTime类)。

然而，如果你确实希望使用java.util.Date，我建议写一个实用方法;如。

public static Date setTimeToMidnight(Date date) {
    Calendar calendar = Calendar.getInstance();

    calendar.setTime( date );
    calendar.set(Calendar.HOUR_OF_DAY, 0);
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);
    calendar.set(Calendar.MILLISECOND, 0);

    return calendar.getTime();
}

public Date saveDateWithoutTime(Date date) {
    Calendar calendar = Calendar.getInstance();

    calendar.setTime( date );
    calendar.set(Calendar.HOUR_OF_DAY, 0);
    calendar.set(Calendar.HOUR, 0);
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);
    calendar.set(Calendar.MILLISECOND, 0);

    return calendar.getTime();
}

这将帮助你在不考虑时间的情况下比较日期。

这里有一个来自这个博客的解决方案:http://brigitzblog.blogspot.com/2011/10/java-compare-dates.html

long milliseconds1 = calendar1.getTimeInMillis();
long milliseconds2 = calendar2.getTimeInMillis();
long diff = milliseconds2 - milliseconds1;
long diffDays = diff / (24 * 60 * 60 * 1000);
System.out.println("Time in days: " + diffDays  + " days.");

也就是说，你可以看到以毫秒为单位的时间差是否小于一天的长度。