@Override
    public DefaultServiceConfigSetters decorator(
            Function<? super HttpService, ? extends HttpService> decorator) {
        requireNonNull(decorator, "decorator");
        if (this.decorator != null) {
            this.decorator = this.decorator.andThen(decorator);
        } else {
            this.decorator = decorator;
        }
        return this;
    }
A default implementation of {@link ServiceConfigSetters} that stores service related settings
and provides a method {@link DefaultServiceConfigSetters#toServiceConfigBuilder(Route, String, HttpService)}
to build {@link ServiceConfigBuilder}.
core/src/main/java/com/linecorp/armeria/server/DefaultServiceConfigSetters.java