public static String checkIPs(String... ips) {
        
        if (ips == null || ips.length == 0) {
            
            return CHECK_OK;
        }
        // illegal response
        StringBuilder illegalResponse = new StringBuilder();
        for (String ip : ips) {
            if (InternetAddressUtil.isIP(ip)) {
                continue;
            }
            illegalResponse.append(ip).append(",");
        }
        
        if (illegalResponse.length() == 0) {
            return CHECK_OK;
        }
        
        return ILLEGAL_IP_PREFIX + illegalResponse.substring(0, illegalResponse.length() - 1);
    }
@Test
    void testCheckIPs() {
        assertEquals("ok", InternetAddressUtil.checkIPs("127.0.0.1"));
        assertEquals("ok", InternetAddressUtil.checkIPs());
        assertEquals("ok", InternetAddressUtil.checkIPs());
        assertEquals("ok", InternetAddressUtil.checkIPs(null));
        
        assertEquals("illegal ip: 127.100.19", InternetAddressUtil.checkIPs("127.100.19", "127.0.0.1"));
    }