I started learning spring’s reactive http client WebClient and im having trouble understanding contextual information between requests and responses. When using RestTemplate this was easy to do with thread locals.

I want to implement a generic webclient that adds callId to the request and response logs automatically so i tried something like this which throws an error because “callId” is not in the context:

  private WebClient createLoggingWebclient() {
    return WebClient.builder()
      .filter(addToCtx())
      .filter(readCtx())
      .baseUrl("https://localhost:8080")
      .build();
  }

  private ExchangeFilterFunction readCtx() {
    return ExchangeFilterFunction.ofResponseProcessor(
      clientResponse ->
        clientResponse.bodyToMono(String.class)
          .flatMap(s ->
            Mono.deferContextual(ctx -> {
              // log response body and callId
              log.info("callId: {}", (String)ctx.get(CALL_ID));
              return Mono.just(clientResponse.mutate().body(s).build());
            })
          )
    );
  }

  private ExchangeFilterFunction addToCtx() {
    return ExchangeFilterFunction.ofRequestProcessor(
      clientRequest ->
        // log request body and callId
        Mono.just(clientRequest).contextWrite(Context.of(CALL_ID, "123"))
    );
  }

What am i getting wrong and how can i implement this feature?