获取当前凌晨时间戳

注意点：在时间的时候注意时区处理，TimeZone.getDefault().getRawOffset()如果在中国则是东8区(8*3600)。建议写成：TimeZone.getDefault().getRawOffset()

//当天日期
    Date date = new Date();
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
    String today = simpleDateFormat.format(date.getTime());
    System.out.println("当天日期" + today);

    //1、当天凌晨(毫秒)
    long daytime1 = simpleDateFormat.parse(today).getTime();
    System.out.println("1、当天凌晨(毫秒)" + daytime1);

    //2、当天凌晨(毫秒)
    long current = System.currentTimeMillis();
    long daytime2 = current-(current+ TimeZone.getDefault().getRawOffset())%(1000*3600*24);
    System.out.println("2、当天凌晨(毫秒)" + daytime2);

    //3、当天凌晨(毫秒)
    Calendar c = Calendar.getInstance();
    c.set(Calendar.HOUR_OF_DAY, 0);
    c.set(Calendar.MINUTE, 0);
    c.set(Calendar.SECOND, 0);
    c.set(Calendar.MILLISECOND, 0);
    long daytime3 = c.getTimeInMillis();
    System.out.println("3、当天凌晨(毫秒)" + daytime3);

    //4、当天凌晨(毫秒)
    long now = System.currentTimeMillis() / 1000l;
    long daySecond = 60 * 60 * 24;
    long dayTime4 = (now - (now + 8 * 3600) % daySecond) * 1000 ;
    System.out.println("4、当天凌晨(毫秒)" + dayTime4);