TraceIdFilter.java

@Component
@Slf4j
public class TraceIdFilter implements WebFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        Map<String, String> headers = exchange.getRequest().getHeaders().toSingleValueMap();

        return chain.filter(exchange)
                .subscriberContext(context -> {
                    var traceId = "";
                    if (headers.containsKey("X-B3-TRACEID")) {
                        traceId = headers.get("X-B3-TRACEID");
                        MDC.put("X-B3-TraceId", traceId);
                    } else if (!exchange.getRequest().getURI().getPath().contains("/actuator")) {
                        log.warn("TRACE_ID not present in header: {}", exchange.getRequest().getURI());
                    }

                    // simple hack to provide the context with the exchange, so the whole chain can get the same trace id
                    Context contextTmp = context.put("X-B3-TraceId", traceId);
                    exchange.getAttributes().put("X-B3-TraceId", traceId);

                    return contextTmp;
                });

    }


}