Java logging request id filter

requestIdFilter.java

public class RequestIdFilter implements OrderedWebFilter {
    @Override
    public int getOrder() {
        return REQUEST_WRAPPER_FILTER_MAX_ORDER - 10;
    }

    @Override
    @NonNull
    public Mono<Void> filter(@NonNull ServerWebExchange ex, @NonNull WebFilterChain chain) {
        return
            chain.filter(ex)
                .contextWrite(saveRequestId(ex.getRequest()))
            ;
    }

    private Function<Context,Context> saveRequestId(final ServerHttpRequest request) {
        final var requestId = 
            Optional.ofNullable(request.getHeaders().getFirst("X-Request-Id"))
                .orElseGet(() -> UUID.randomUUID().toString());

        return context -> context.put("requestId", requestId);
    }
}