public static HostFilter from(String hostNames, String flavors, String clusterTypes, String clusterIds) {
        return new HostFilter(
                StringUtilities.split(hostNames),
                StringUtilities.split(flavors),
                StringUtilities.split(clusterTypes).stream().map(ClusterSpec.Type::from).collect(Collectors.toSet()),
                StringUtilities.split(clusterIds).stream().map(ClusterSpec.Id::from).collect(Collectors.toSet()));
    }
Returns a host filter from three comma and-or space separated string lists. The strings may be null or empty.
config-provisioning/src/main/java/com/yahoo/config/provision/HostFilter.java