即使在TraceWebFilter之后注册，TraceId和SpanId在WebFilter中也为null

Question

我目前在Spring Boot中使用2020.0.0，注册了一个自定义web过滤器，该过滤器记录请求中的信息（顺序是webProperties.filterOrder 1，所以应该在TraceWebFilter之后注册）。由于某些原因，traceId和spanId不在MDC中（因此不记录）。

WebFilter实现：

class TraceWebFilter(
        private val webProperties: SleuthWebProperties,
        private val tracer: Tracer
): WebFilter, Ordered {
    override fun getOrder(): Int = webProperties.filterOrder + 1

    override fun filter(exchange: ServerWebExchange, chain: WebFilterChain): Mono<Void> {
        logger.debug { "Building trace web filter" }

        return Mono.defer {
            MDC.put("Request-Method", exchange.request.method?.toString())
            MDC.put("Request-Path", exchange.request.path.toString())

            logger.info { tracer.currentSpan() }

            logger.info { ">> headers=${exchange.request.headers}" }
            logger.info { ">> method=${exchange.request.method}" }
            logger.info { ">> path=${exchange.request.path}" }

            exchange.response.beforeCommit {
                Mono.fromRunnable {
                    logger.info { "<< headers=${exchange.response.headers}" }
                    logger.info { "<< status=${exchange.response.rawStatusCode}" }
                }
            }

            chain.filter(exchange)
        }
    }
}

日志：

app_1       | 2021-01-28 04:43:24.420 DEBUG [user-service,method=,path=,traceId=,spanId=] 1 --- [p-nio-80-exec-2] o.s.c.s.instrument.web.TraceWebFilter    : Received a request to uri [/users]
app_1       | 2021-01-28 04:43:24.566 DEBUG [user-service,method=,path=,traceId=,spanId=] 1 --- [p-nio-80-exec-2] o.s.c.s.instrument.web.TraceWebFilter    : Handled receive of span RealSpan(9b7383611e5a3bc2/9b7383611e5a3bc2)
app_1       | 2021-01-28 04:43:24.633 DEBUG [user-service,method=,path=,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : Building trace web filter
app_1       | 2021-01-28 04:43:24.638  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : null
app_1       | 2021-01-28 04:43:24.694  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : >> headers=[content-type:"application/json", user-agent:"PostmanRuntime/7.26.8", accept:"*/*", cache-control:"no-cache", postman-token:"18d99e30-ce7a-4659-a2c1-21020d8bf2b5", host:"localhost:9100", accept-encoding:"gzip, deflate, br", connection:"keep-alive", content-length:"2"]
app_1       | 2021-01-28 04:43:24.699  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : >> method=POST
app_1       | 2021-01-28 04:43:24.747  INFO [user-service,method=POST,path=/users,traceId=,spanId=] 1 --- [p-nio-80-exec-2] c.p.p.components.tracing.TraceWebFilter  : >> path=/users

请注意以下内容：

• 日志中的traceId和spanId为空
• 日志tracer.currentSpan in log is null

有什么线索说明为什么会这样吗？

Answer 1

如果您查看TraceWebFilter，您将看到它没有将任何内容放入MDC（MDC基本上是一个线程局部，您处于一个异步事件循环）。

>

但它与跟踪器进行交互，您也可以将跟踪器注入到过滤器中，并从中获取当前跨度：跟踪器。currentSpan（），从Span的TraceContext可以得到traceId和spanId。

此外，它将Span放入Exchange属性中：

this.exchange.getAttributes().put(TRACE_REQUEST_ATTR, span);

我建议将跟踪程序注入过滤器中，并从中获取当前Span。