What is the correct way of using Spring-Reactor's changeRequestUri()?

Question

Could someone please provide an example and an explanation of how this method is used? I am new to project Reactor and I have difficulty getting my head around the way to use it, plus there dont seem to be enough tutorials out there. What I want is to call a service that will return a hostname in String format which I then want to user as uri

This is the method's package and the method:

org.springframework.cloud.gateway.route.builder



/**
 * A filter which change the URI the request will be routed to by the Gateway.
 * @param determineRequestUri a {@link Function} which takes a
 * {@link ServerWebExchange} and returns a URI to route the request to
 * @return a {@link GatewayFilterSpec} that can be used to apply additional filters
 */
public GatewayFilterSpec changeRequestUri(Function<ServerWebExchange, Optional<URI>> determineRequestUri) {
    return filter(new AbstractChangeRequestUriGatewayFilterFactory<Object>(Object.class) {
        @Override
        protected Optional<URI> determineRequestUri(ServerWebExchange exchange, Object config) {
            return determineRequestUri.apply(exchange);
        }
    }.apply(c -> {
    }));
}