Date now = new Date();
Calendar cal1 = Calendar.getInstance();
cal1.setTime(now);
// 将时分秒,毫秒域清零
cal1.set(Calendar.HOUR_OF_DAY, 0);
cal1.set(Calendar.MINUTE, 0);
cal1.set(Calendar.SECOND, 0);
cal1.set(Calendar.MILLISECOND, 0);
System.out.printf("%1$tF %1$tT\n", cal1.getTime());// cal1.getTime()返回的Date已经是更新后的对象
