java 当年当月当天的时间戳

        Calendar isthismonth = Calendar.getInstance();
        isthismonth.add(Calendar.MONTH, 1);
        isthismonth.set(Calendar.DAY_OF_MONTH, 1);
        isthismonth.set(Calendar.HOUR_OF_DAY, 0);
        isthismonth.set(Calendar.MINUTE, 0);
        isthismonth.set(Calendar.SECOND, 0);
        isthismonth.set(Calendar.MILLISECOND, 0);
        Long isthismonth1 = isthismonth.getTimeInMillis() / 1000;

        Calendar isthisyear = Calendar.getInstance();
        isthisyear.add(Calendar.YEAR, 1);
        isthisyear.set(Calendar.MONTH, 0);
        isthisyear.set(Calendar.DAY_OF_MONTH, 1);
        isthisyear.set(Calendar.HOUR_OF_DAY, 0);
        isthisyear.set(Calendar.MINUTE, 0);
        isthisyear.set(Calendar.SECOND, 0);
        isthisyear.set(Calendar.MILLISECOND, 0);
        Long isthisyear1 = isthisyear.getTimeInMillis() / 1000;

        Calendar isthisday = Calendar.getInstance();
        isthisday.add(Calendar.DATE, 1);
        isthisday.set(Calendar.HOUR_OF_DAY, 0);
        isthisday.set(Calendar.MINUTE, 0);
        isthisday.set(Calendar.SECOND, 0);
        isthisday.set(Calendar.MILLISECOND, 0);
        Long isthisday1 = isthisday.getTimeInMillis() / 1000;