如何结合Micrometer的@Observed与B3 Trace ID并注入方法？

核心思路 #

要把B3-Trace-ID和@Observed注解生成的观测Span关联，本质是把B3的追踪标识注入到Micrometer的Span上下文或标签中，主要有三种落地方式：

1. 直接给观测Span添加B3标签（快速实现）

在被@Observed注解的方法内部，通过Micrometer的TracerAPI获取当前Span，手动添加B3-Trace-ID标签，这样观测数据里就能直接看到关联的追踪ID。

import io.micrometer.tracing.Tracer;
import io.micrometer.observation.annotation.Observed;
import org.springframework.stereotype.Component;

@Component
public class BusinessService {
    private final Tracer tracer;

    public BusinessService(Tracer tracer) {
        this.tracer = tracer;
    }

    @Observed(name = "order.process")
    public void processOrder(String b3TraceId) {
        // 将B3 Trace-ID绑定到当前观测Span
        if (tracer.currentSpan() != null) {
            tracer.currentSpan().tag("b3.trace.id", b3TraceId);
        }
        // 业务逻辑代码...
    }
}

2. 自动关联到追踪上下文（链路打通）

如果项目集成了Micrometer Tracing的B3适配，可在请求入口（过滤器/拦截器）解析B3头并构建TraceContext，后续@Observed方法生成的Span会自动继承这个Trace-ID，实现网络调用与方法观测链路的完全串联。

import io.micrometer.tracing.TraceContext;
import io.micrometer.tracing.TraceContextBuilder;
import io.micrometer.tracing.Tracer;
import jakarta.servlet.Filter;
import jakarta.servlet.FilterChain;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.http.HttpServletRequest;
import org.springframework.stereotype.Component;

@Component
public class B3TraceContextFilter implements Filter {
    private final Tracer tracer;

    public B3TraceContextFilter(Tracer tracer) {
        this.tracer = tracer;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
        HttpServletRequest httpReq = (HttpServletRequest) request;
        String b3TraceId = httpReq.getHeader("B3-Trace-ID");
        String b3SpanId = httpReq.getHeader("B3-Span-ID");

        if (b3TraceId != null) {
            // 构建包含B3标识的TraceContext
            TraceContext traceContext = TraceContextBuilder.create()
                    .traceId(b3TraceId)
                    .spanId(b3SpanId != null ? b3SpanId : tracer.nextSpan().context().spanId())
                    .build();
            // 将上下文绑定到当前线程，后续@Observed方法自动复用
            try (Tracer.SpanInScope ignored = tracer.withSpan(tracer.nextSpan(traceContext))) {
                chain.doFilter(request, response);
            }
        } else {
            chain.doFilter(request, response);
        }
    }
}

3. 切面统一处理（批量方法适配）

如果多个@Observed方法都需要关联B3-Trace-ID，可自定义切面拦截所有被@Observed注解的方法，统一注入标签，避免重复代码。

import io.micrometer.tracing.Tracer;
import io.micrometer.observation.annotation.Observed;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;
import jakarta.servlet.http.HttpServletRequest;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

@Aspect
@Component
public class ObservedMethodB3Aspect {
    private final Tracer tracer;

    public ObservedMethodB3Aspect(Tracer tracer) {
        this.tracer = tracer;
    }

    @Before("@annotation(Observed)")
    public void injectB3TraceId(JoinPoint joinPoint) {
        ServletRequestAttributes attrs = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        if (attrs != null) {
            HttpServletRequest request = attrs.getRequest();
            String b3TraceId = request.getHeader("B3-Trace-ID");
            if (b3TraceId != null && tracer.currentSpan() != null) {
                tracer.currentSpan().tag("b3.trace.id", b3TraceId);
            }
        }
    }
}

方案选择建议 #

• 仅需在观测数据中标记B3 ID：选方法内加标签的方式；
• 需要打通网络调用与方法观测的完整链路：选入口处绑定TraceContext的方式；
• 大量方法需要统一处理：选切面方案。

内容的提问来源于stack exchange，提问作者Dmytro Nasyrov