public static String toString(long unixTime, String pattern) {
        return Instant.ofEpochSecond(unixTime).atZone(ZoneId.systemDefault()).format(DateTimeFormatter.ofPattern(pattern));
    }
@Test
    public void testToString3() {
        String dateStr = DateKit.toString(localDateTime, "yyyy-MM-dd");
        String timeStr = DateKit.toString(localDateTime, "yyyy-MM-dd HH:mm:ss");
        Assert.assertEquals("2017-09-20", dateStr);
        Assert.assertEquals("2017-09-20 15:20:10", timeStr);
    }