public static HostAndPort fromString(String hostPort, int defaultPort) {
    if (hostPort == null) throw new NullPointerException("hostPort == null");

    String host = hostPort;
    int endHostIndex = hostPort.length();
    if (hostPort.startsWith("[")) { // Bracketed IPv6
      endHostIndex = hostPort.lastIndexOf(']') + 1;
      host = hostPort.substring(1, endHostIndex == 0 ? 1 : endHostIndex - 1);
      if (!Endpoint.newBuilder().parseIp(host)) { // reuse our IPv6 validator
        throw new IllegalArgumentException(hostPort + " contains an invalid IPv6 literal");
      }
    } else {
      int colonIndex = hostPort.indexOf(':'), nextColonIndex = hostPort.lastIndexOf(':');
      if (colonIndex >= 0) {
        if (colonIndex == nextColonIndex) { // only 1 colon
          host = hostPort.substring(0, colonIndex);
          endHostIndex = colonIndex;
        } else if (!Endpoint.newBuilder().parseIp(hostPort)) { // reuse our IPv6 validator
          throw new IllegalArgumentException(hostPort + " is an invalid IPv6 literal");
        }
      }
    }
    if (host.isEmpty()) throw new IllegalArgumentException(hostPort + " has an empty host");
    if (endHostIndex + 1 < hostPort.length() && hostPort.charAt(endHostIndex) == ':') {
      return new HostAndPort(host, validatePort(hostPort.substring(endHostIndex + 1), hostPort));
    }
    return new HostAndPort(host, defaultPort);
  }
Constructs a host-port pair from the given string, defaulting to the indicated port if absent
zipkin-storage/cassandra/src/main/java/zipkin2/storage/cassandra/internal/HostAndPort.java