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实现原理

api入口或者网关处生成traceId，调用服务时优先检查是否头部带有traceId，有则复用，没有则生成

实现方式

处理api相关traceId

1.通过filter复用或者生成traceId，并且将traceId输入到响应头中

import java.io.IOException;
import java.util.UUID;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.slf4j.MDC;
import org.springframework.web.filter.OncePerRequestFilter;public class TraceIdFilter extends OncePerRequestFilter {public TraceIdFilter() {}protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {String traceId = request.getHeader("X-Trace-Id");if (traceId == null) {traceId = this.generateTraceId();}MDC.put("traceId", traceId);response.setHeader("X-Trace-Id", traceId);try {filterChain.doFilter(request, response);} finally {MDC.clear();}}private String generateTraceId() {return UUID.randomUUID().toString().replace("-", "");}
}

 2、在对应项目中启用filter

@Configuration
public class WebFilterConfig {@Beanpublic FilterRegistrationBean<TraceIdFilter> loggingFilter() {FilterRegistrationBean<TraceIdFilter> registrationBean = new FilterRegistrationBean<>();registrationBean.setFilter(new TraceIdFilter());registrationBean.addUrlPatterns("/*"); // 只对特定 URL 匹配return registrationBean;}
}

Feign调用时传递traceId

1、声明拦截器（feign调用时从mdc获取traceId放入请求头中）

import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.slf4j.MDC;public class FeIgnMCDInterceptor implements RequestInterceptor {public FeIgnMCDInterceptor() {}public void apply(RequestTemplate template) {String traceId = MDC.get("traceId");if (traceId != null) {template.header("X-Trace-Id", new String[]{traceId});}}
}

2、启用拦截器

// 任意位置注册为springbean即可
@Bean
public FeIgnMCDInterceptor feIgnMCDInterceptor() {return new FeIgnMCDInterceptor();
}

日志配置文件中打印traceId

<!-- 日志输出格式 -->
<property name="log.pattern" value="%d{yyyy-MM-dd HH:mm:ss.SSS} [${application_name}] [%X{traceId}] [%thread] %-5level %logger - [%method,%line] - %msg%n" />