public static String getCityCodeByIdCard(String idcard) {
		int len = idcard.length();
		if (len == CHINA_ID_MIN_LENGTH || len == CHINA_ID_MAX_LENGTH) {
			return idcard.substring(0, 4);
		}
		return null;
	}
@Test
	public void getCityCodeByIdCardTest() {
		String codeByIdCard = IdcardUtil.getCityCodeByIdCard(ID_18);
		assertEquals("3210", codeByIdCard);
	}