1.日期格式的

                Calendar calendar = Calendar.getInstance();
                calendar.setTime(new Date());
                calendar.set(Calendar.HOUR_OF_DAY, 0);
                calendar.set(Calendar.MINUTE, 0);
                calendar.set(Calendar.SECOND, 0);
                Date zero = calendar.getTime();

2.時間戳

                long current = System.currentTimeMillis();
                long zero = current/(1000*3600*24)*(1000*3600*24) - TimeZone.getDefault().getRawOffset();

public static void main(String[] args) {
        long current=System.currentTimeMillis();//當前時間毫秒數
        long zero=current/(1000*3600*24)*(1000*3600*24)-TimeZone.getDefault().getRawOffset();//今天零點零分零秒的毫秒數
        long twelve=zero+24*60*60*1000-1;//今天23點59分59秒的毫秒數
        long yesterday=System.currentTimeMillis()-24*60*60*1000;//昨天的這一時間的毫秒數
        System.out.println(new Timestamp(current));//當前時間
        System.out.println(new Timestamp(yesterday));//昨天這一時間點
        System.out.println(new Timestamp(zero));//今天零點零分零秒
        System.out.println(new Timestamp(twelve));//今天23點59分59秒
}

http://www.cnblogs.com/cc-java/p/6699045.html

獲取當天（今日）零點零分零秒