@Override
    public ServerBuilder decoratorUnder(String prefix,
                                        Function<? super HttpService, ? extends HttpService> decorator) {
        virtualHostTemplate.decoratorUnder(prefix, decorator);
        return this;
    }
Decorates {@link HttpService}s under the specified directory.
The specified decorator(s) is/are executed in reverse order of the insertion.
core/src/main/java/com/linecorp/armeria/server/ServerBuilder.java