SpringCloud sleuth 应用内 traceId 获取及使用

一、maven 依赖

    org.springframework.cloud
    spring-cloud-starter-sleuth

二、获取代码

// ServletServerHttpRequest request
TraceContext traceContext = (TraceContext) request.getServletRequest().getAttribute(TraceContext.class.getName());
String traceId = traceContext.traceIdString();

// HttpServletRequest request
TraceContext traceContext = (TraceContext) request.getAttribute(TraceContext.class.getName());
String traceId = traceContext.traceIdString();

三、为何可以如此获取？

// brave.servlet.TracingFilter

...
...

public final class TracingFilter implements Filter {
    final ServletRuntime servlet = ServletRuntime.get();
    final CurrentTraceContext currentTraceContext;
    final HttpServerHandler handler;

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest)request;
        HttpServletResponse res = this.servlet.httpServletResponse(response);
        TraceContext context = (TraceContext)request.getAttribute(TraceContext.class.getName());
        if (context != null) {
            CurrentTraceContext.Scope scope = this.currentTraceContext.maybeScope(context);

            try {
                chain.doFilter(request, response);
            } finally {
                scope.close();
            }

        } else {
            Span span = this.handler.handleReceive(new HttpServletRequestWrapper(req));
            request.setAttribute(SpanCustomizer.class.getName(), span.customizer());
            // 赋值 traceId 
            request.setAttribute(TraceContext.class.getName(), span.context());
        ...
        ...
            
        }
    }

}

四、实际项目中使用

package com.zxguan.springcloud2.user.config;

import org.springframework.core.MethodParameter;
import org.springframework.core.annotation.Order;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;

@Order(0)
@RestControllerAdvice
public class ApiResponseAdvice implements ResponseBodyAdvice {

    /**
     * 判断需要处理的情况
     *
     * @param methodParameter
     * @param selectedHttpMessageConverter
     *
     * @return boolean true:   false:
     */
    @Override
    public boolean supports(MethodParameter methodParameter, Class selectedHttpMessageConverter) {
        // 
        return false;
    }


    /**
     * 消息体返回前处理
     *
     * @param body                         返回的消息体
     * @param methodParameter              响应类型
     * @param mediaType                    请求的响应 contentType
     * @param selectedHttpMessageConverter 执行序列化的转换器
     * @param request
     * @param response
     *
     * @return Object 返回的消息体
     */
    @Override
    public Object beforeBodyWrite(Object body, MethodParameter methodParameter, MediaType mediaType, Class selectedHttpMessageConverter, ServerHttpRequest request, ServerHttpResponse response) {
        // 此处可以统一添加 traceId 到响应中
        return null;
    }

}

五、日志中打印 traceId 

// 借助 MDC 机制, 实现 traceId 的打印
%d{yyyy-MM-dd HH:mm:ss.SSS} %X{X-B3-TraceId:-}

六、特别注意

MDC traceId 设置, 可以通过自定义过滤器提前到过滤器级别，但需要注意过滤器顺序，自定义过滤器需排在 brave.servlet.TracingFilter 之后