private static Mapping<String, VirtualHost> buildDomainMapping(VirtualHost defaultVirtualHost,
                                                                   List<VirtualHost> virtualHosts) {
        // Set virtual host definitions and initialize their domain name mapping.
        final DomainMappingBuilder<VirtualHost> mappingBuilder = new DomainMappingBuilder<>(defaultVirtualHost);
        for (VirtualHost h : virtualHosts) {
            if (h.port() > 0) {
                // A port-based virtual host will be handled by buildDomainAndPortMapping().
                continue;
            }
            mappingBuilder.add(h.hostnamePattern(), h);
        }
        return mappingBuilder.build();
    }
Initialized later by {@link Server} via {@link #setServer(Server)}.
core/src/main/java/com/linecorp/armeria/server/DefaultServerConfig.java