获取当天（今日）零点零分零秒

                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();

                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();//当前时间毫秒数
        long zero=current/(1000*3600*24)*(1000*3600*24)-TimeZone.getDefault().getRawOffset();//今天零点零分零秒的毫秒数
        long twelve=zero+24*60*60*1000-1;//今天23点59分59秒的毫秒数
        long yesterday=System.currentTimeMillis()-24*60*60*1000;//昨天的这一时间的毫秒数
        System.out.println(new Timestamp(current));//当前时间
        System.out.println(new Timestamp(yesterday));//昨天这一时间点
        System.out.println(new Timestamp(zero));//今天零点零分零秒
        System.out.println(new Timestamp(twelve));//今天23点59分59秒
}