@Override
    public VirtualHost findVirtualHost(String hostname, int port) {
        if (virtualHostAndPortMapping == null) {
            return defaultVirtualHost;
        }

        final Mapping<String, VirtualHost> virtualHostMapping = virtualHostAndPortMapping.get(port);
        if (virtualHostMapping != null) {
            final VirtualHost virtualHost = virtualHostMapping.map(hostname + ':' + port);
            // Exclude the default virtual host from port-based virtual hosts.
            if (virtualHost != defaultVirtualHost) {
                return virtualHost;
            }
        }
        // No port-based virtual host is configured. Look for named-based virtual host.
        final Mapping<String, VirtualHost> nameBasedMapping = virtualHostAndPortMapping.get(-1);
        assert nameBasedMapping != null;
        return nameBasedMapping.map(hostname);
    }
Initialized later by {@link Server} via {@link #setServer(Server)}.
core/src/main/java/com/linecorp/armeria/server/DefaultServerConfig.java