public static String indexToColName(int index) {
		if (index < 0) {
			return null;
		}
		final StringBuilder colName = StrUtil.builder();
		do {
			if (colName.length() > 0) {
				index--;
			}
			int remainder = index % 26;
			colName.append((char) (remainder + 'A'));
			index = (index - remainder) / 26;
		} while (index > 0);
		return colName.reverse().toString();
	}
@Test
	public void indexToColNameTest() {
		assertEquals("A", ExcelUtil.indexToColName(0));
		assertEquals("B", ExcelUtil.indexToColName(1));
		assertEquals("C", ExcelUtil.indexToColName(2));

		assertEquals("AA", ExcelUtil.indexToColName(26));
		assertEquals("AB", ExcelUtil.indexToColName(27));
		assertEquals("AC", ExcelUtil.indexToColName(28));

		assertEquals("AAA", ExcelUtil.indexToColName(702));
		assertEquals("AAB", ExcelUtil.indexToColName(703));
		assertEquals("AAC", ExcelUtil.indexToColName(704));
	}