如何在 spring-webflux WebFilter 中正确使用 slf4j MDC

以下是一个基于最新方法的解决方案，截至2021年5月，取自官方文档：

import java.util.List;
import java.util.Optional;
import java.util.UUID;
import java.util.function.Consumer;
import lombok.extern.slf4j.Slf4j;
import org.slf4j.MDC;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.HttpHeaders;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import reactor.core.publisher.Mono;
import reactor.core.publisher.Signal;
import reactor.util.context.Context;

@Slf4j
@Configuration
public class RequestIdFilter implements WebFilter {

  @Override
  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
    ServerHttpRequest request = exchange.getRequest();
    String requestId = getRequestId(request.getHeaders());
    return chain
        .filter(exchange)
        .doOnEach(logOnEach(r -> log.info("{} {}", request.getMethod(), request.getURI())))
        .contextWrite(Context.of("CONTEXT_KEY", requestId));
  }

  private String getRequestId(HttpHeaders headers) {
    List<String> requestIdHeaders = headers.get("X-Request-ID");
    return requestIdHeaders == null || requestIdHeaders.isEmpty()
        ? UUID.randomUUID().toString()
        : requestIdHeaders.get(0);
  }

  public static <T> Consumer<Signal<T>> logOnEach(Consumer<T> logStatement) {
    return signal -> {
      String contextValue = signal.getContextView().get("CONTEXT_KEY");
      try (MDC.MDCCloseable cMdc = MDC.putCloseable("MDC_KEY", contextValue)) {
        logStatement.accept(signal.get());
      }
    };
  }

  public static <T> Consumer<Signal<T>> logOnNext(Consumer<T> logStatement) {
    return signal -> {
      if (!signal.isOnNext()) return;
      String contextValue = signal.getContextView().get("CONTEXT_KEY");
      try (MDC.MDCCloseable cMdc = MDC.putCloseable("MDC_KEY", contextValue)) {
        logStatement.accept(signal.get());
      }
    };
  }
}

假设您在：application.properties

logging.pattern.level=[%X{MDC_KEY}] %5p

那么每次调用端点时，您的服务器日志都将包含如下日志：

2021-05-06 17:07:41.852 [60b38305-7005-4a05-bac7-ab2636e74d94]  INFO 20158 --- [or-http-epoll-6] my.package.RequestIdFilter    : GET http://localhost:12345/my-endpoint/444444/

每次你想在反应式上下文中手动记录某些内容时，你都会将以下内容添加到你的反应式链中：

.doOnEach(logOnNext(r -> log.info("Something")))

如果希望将 传播到其他服务以进行分布式跟踪，则需要从反应式上下文（而不是从 MDC）读取它，并使用以下内容包装代码：X-Request-IDWebClient

Mono.deferContextual(
    ctx -> {
      RequestHeadersSpec<?> request = webClient.get().uri(uri);
      request = request.header("X-Request-ID", ctx.get("CONTEXT_KEY"));
      // The rest of your request logic...
    });

你可以做类似下面的事情，你可以用你喜欢的任何类来设置，对于这个例子，我只使用了头 - 但是自定义类会做得很好。如果在此处设置它，则任何具有处理程序等的日志记录也将有权访问 .
下面，设置 MDC 并在之后将其清除。显然，这可以用您喜欢的任何东西替换。contextcontextlogWithContext

public class RequestIdFilter  implements WebFilter {

    private Logger LOG = LoggerFactory.getLogger(RequestIdFilter.class);

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        HttpHeaders headers = exchange.getRequest().getHeaders();
        return chain.filter(exchange)
                .doAfterSuccessOrError((r, t) -> logWithContext(headers, httpHeaders -> LOG.info("Some message with MDC set")))
                .subscriberContext(Context.of(HttpHeaders.class, headers));
    }

    static void logWithContext(HttpHeaders headers, Consumer<HttpHeaders> logAction) {
        try {
            headers.forEach((name, values) -> MDC.put(name, values.get(0)));
            logAction.accept(headers);
        } finally {
            headers.keySet().forEach(MDC::remove);
        }

    }

}