Apache commons-lang几乎无处不在。那么这个呢?

if (DateUtils.isSameDay(date1, date2)) {
    // it's same
} else if (date1.before(date2)) {
   // it's before
} else {
   // it's after
}

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();
}

如果你只想比较两个没有时间的日期，那么下面的代码可能会帮助你:

final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
Date dLastUpdateDate = dateFormat.parse(20111116);
Date dCurrentDate = dateFormat.parse(dateFormat.format(new Date()));
if (dCurrentDate.after(dLastUpdateDate))
{
   add your logic
}

Apache commons-lang几乎无处不在。那么这个呢?

if (DateUtils.isSameDay(date1, date2)) {
    // it's same
} else if (date1.before(date2)) {
   // it's before
} else {
   // it's after
}

对这个替代方案有什么意见吗?

SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
sdf.format(date1).equals(sdf.format(date2));

另一个简单的比较方法是基于这里的答案和我的导师的指导

public static int compare(Date d1, Date d2) {
    Calendar c1 = Calendar.getInstance();
    Calendar c2 = Calendar.getInstance();
    c1.setTime(d1);
    c1.set(Calendar.MILLISECOND, 0);
    c1.set(Calendar.SECOND, 0);
    c1.set(Calendar.MINUTE, 0);
    c1.set(Calendar.HOUR_OF_DAY, 0);
    c2.setTime(d2);
    c2.set(Calendar.MILLISECOND, 0);
    c2.set(Calendar.SECOND, 0);
    c2.set(Calendar.MINUTE, 0);
    c2.set(Calendar.HOUR_OF_DAY, 0);
    return c1.getTime().compareTo(c2.getTime());
  }

编辑: 根据@Jonathan Drapeau的说法，上面的代码在某些情况下会失败(我想看看这些情况)，他建议如下:

public static int compare2(Date d1, Date d2) {
    Calendar c1 = Calendar.getInstance();
    Calendar c2 = Calendar.getInstance();
    c1.clear();
    c2.clear();
    c1.set(Calendar.YEAR, d1.getYear());
    c1.set(Calendar.MONTH, d1.getMonth());
    c1.set(Calendar.DAY_OF_MONTH, d1.getDay());
    c2.set(Calendar.YEAR, d2.getYear());
    c2.set(Calendar.MONTH, d2.getMonth());
    c2.set(Calendar.DAY_OF_MONTH, d2.getDay());
    return c1.getTime().compareTo(c2.getTime());
}

请注意，Date类已弃用，因为它不适合国际化。取而代之的是Calendar类!