万字长文：深入 Spring Cloud Alibaba 源码，解密微服务调用链路体系

// opentelemetry-spring-starter: io.opentelemetry.instrumentation.spring.autoconfigure.OpenTelemetryAutoConfiguration

@Bean
@ConditionalOnMissingBean
public Tracer tracer(OpenTelemetry openTelemetry) {
    // 1. 从全局 OpenTelemetry 实例中获取 Tracer
    return openTelemetry.getTracer("io.opentelemetry.spring");
}

@Bean
@ConditionalOnMissingBean
public OpenTelemetry openTelemetry(
        ConfigProperties config,
        @Autowired(required = false) Resource resource,
        @Autowired(required = false) List<SpanExporter> spanExporters,
        @Autowired(required = false) List<MetricExporter> metricExporters) {
    
    // 2. 构建 OpenTelemetry SDK 实例
    SdkTracerProviderBuilder tracerProviderBuilder = SdkTracerProvider.builder();
    
    // 3. 注册 Span Exporter (如 OTLP, Jaeger)
    if (!spanExporters.isEmpty()) {
        tracerProviderBuilder.addSpanProcessor(
            BatchSpanProcessor.builder(spanExporters.get(0)).build()
        );
    }
    
    // 4. 构建全局 OpenTelemetry 实例
    OpenTelemetrySdk sdk = OpenTelemetrySdk.builder()
        .setTracerProvider(tracerProviderBuilder.build())
        .setPropagators(ContextPropagators.create(W3CTraceContextPropagator.getInstance()))
        .buildAndRegisterGlobal();
    
    return sdk;
}

// opentelemetry-java-instrumentation: FeignClientBeanPostProcessor

public Object postProcessAfterInitialization(Object bean, String beanName) {
    if (bean instanceof FeignClientFactoryBean) {
        FeignClientFactoryBean factory = (FeignClientFactoryBean) bean;
        // 1. 获取原始的 Builder
        feign.Builder builder = factory.getBuilder();
        if (builder == null) {
            builder = Feign.builder();
        }
        // 2. 用 OpenTelemetry 的拦截器包装 Builder
        factory.setBuilder(
            builder
                .requestInterceptor(new OpenTelemetryFeignRequestInterceptor(tracer))
                .client(new OpenTelemetryFeignClient(tracer, factory.getClient()))
        );
    }
    return bean;
}

public void apply(RequestTemplate template) {
    // 1. 获取当前活跃的 Span (即上游服务传来的 Context)
    Context current = Context.current();
    
    // 2. 创建一个新的 CLIENT Span，代表这次 Feign 调用
    Span span = tracer.spanBuilder(template.method() + " " + template.url())
        .setParent(current) // 设置父 Span
        .setAttribute(SemanticAttributes.HTTP_METHOD, template.method())
        .startSpan();
    
    // 3. 将新的 Span 放入 Context，并激活
    try (Scope scope = current.with(span).makeCurrent()) {
        // 4. 【关键】注入追踪信息到 HTTP Header
        TextMapPropagator propagator = GlobalOpenTelemetry.getPropagators().getTextMapPropagator();
        propagator.inject(Context.current(), template, RequestTemplate::header);
    }
    
    // 注意：Span 的结束会在 Response 处理时完成
}

// spring-cloud-starter-alibaba-sentinel: SentinelWebAutoConfiguration

@Bean
@ConditionalOnProperty(name = "spring.cloud.sentinel.filter.enabled", matchIfMissing = true)
public FilterRegistrationBean<SentinelWebMvcFilter> sentinelWebMvcFilter(
        SentinelProperties properties) {
    // 注册一个 Servlet Filter
    FilterRegistrationBean<SentinelWebMvcFilter> registration = new FilterRegistrationBean<>();
    registration.setFilter(new SentinelWebMvcFilter());
    // ...
    return registration;
}

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    String resourceName = getResourceName(httpRequest); // 通常是 URL path
    
    Entry entry = null;
    try {
        // 1. 【Sentinel 核心】尝试进入资源
        entry = SphU.entry(resourceName, EntryType.INBOUND, 1, request);
        
        // 2. 【关键】获取当前 OTel Span
        Span currentSpan = Span.fromContextOrNull(Context.current());
        if (currentSpan != null) {
            // 3. 将 Sentinel 的 block 事件与 Span 关联
            entry.whenBlock(BlockException.class, e -> {
                // 当发生限流/熔断时，更新 Span 状态
                currentSpan.setStatus(StatusCode.ERROR, e.getClass().getSimpleName());
                currentSpan.setAttribute("sentinel.blocked", true);
                currentSpan.setAttribute("sentinel.rule", e.getRule().toString());
            });
        }
        
        chain.doFilter(request, response);
    } catch (BlockException ex) {
        // 4. 处理被 Sentinel Block 的情况
        handleBlockException(httpRequest, (HttpServletResponse) response, ex);
    } finally {
        if (entry != null) {
            entry.exit(); // 退出资源
        }
    }
}

// opentelemetry-java-instrumentation: OpenTelemetryHandlerMappingInterceptor

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
    // 1. 从 HTTP Header 中提取 Context
    Context extractedContext = propagator.extract(
        Context.current(),
        request,
        HttpServletRequestGetter.INSTANCE
    );
    
    // 2. 在提取出的 Context 中创建 SERVER Span
    Span serverSpan = tracer.spanBuilder(getSpanName(request))
        .setParent(extractedContext) // 父 Span 就是上游传来的 Span
        .setSpanKind(SpanKind.SERVER)
        .startSpan();
    
    // 3. 将新的 SERVER Span 绑定到当前线程
    Scope scope = extractedContext.with(serverSpan).makeCurrent();
    request.setAttribute(OTEL_SCOPE_ATTRIBUTE, scope);
    
    return true;
}

public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
    // 4. 请求结束时，关闭 Span 和 Scope
    Scope scope = (Scope) request.getAttribute(OTEL_SCOPE_ATTRIBUTE);
    if (scope != null) {
        scope.close();
    }
    Span span = Span.fromContextOrNull(Context.current());
    if (span != null) {
        span.end();
    }
}

[Order-Service] POST /create (SERVER Span)
├── [Order-Service] GET inventory-service/deduct (CLIENT Span)
│   └── [Inventory-Service] GET /deduct (SERVER Span)
│       ├── [Inventory-Service] DB Query (Span from JDBC instrumentation)
│       └── [Inventory-Service] Sentinel Check (隐式体现在 SERVER Span 的 attributes 中)
└── [Order-Service] DB Save Order (Span from JDBC instrumentation)

@Configuration
public class AsyncConfig {
    @Bean("taskExecutor")
    public Executor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        // 关键：设置 TaskDecorator
        executor.setTaskDecorator(new ContextTaskDecorator());
        executor.initialize();
        return executor;
    }
}

@Service
public class OrderService {
    private final Tracer tracer = GlobalOpenTelemetry.getTracer("business");

    public void createOrder(Order order) {
        Span span = tracer.spanBuilder("validate-order").startSpan();
        try (Scope ignored = span.makeCurrent()) {
            span.setAttribute("order.id", order.getId());
            // ... validation logic
        } finally {
            span.end();
        }
    }
}