SpringBoot+LogBack+MDC实现链路追踪

MDC介绍

MDC(Mapped Diagnostic Context，映射调试上下文)是 log4j 、logback及log4j2 提供的一种方便在多线程条件下记录日志的功能。MDC 可以看成是一个与当前线程绑定的哈希表，可以往其中添加键值对。MDC 中包含的内容可以被同一线程中执行的代码所访问。当前线程的子线程会继承其父线程中的 MDC 的内容。当需要记录日志时，只需要从 MDC 中获取所需的信息即可。

API说明：

clear() => 移除所有MDC
get (String key) => 获取当前线程MDC中指定key的值
getContext() => 获取当前线程MDC的MDC
put(String key, Object o) => 往当前线程的MDC中存入指定的键值对
remove(String key) => 删除当前线程MDC中指定的键值对。

MDC使用

拦截器

@Component
public class LogInterceptor implements HandlerInterceptor
{
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //如果有上层调用就用上层的ID
        String traceId = request.getHeader(TraceIdUtil.TRACE_ID);
        if (StringUtil.isEmpty(traceId)) 
        {
            TraceIdUtil.setTraceId(TraceIdUtil.generateTraceId());
        }
        else
        {
            TraceIdUtil.setTraceId(traceId);
        }
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
            throws Exception 
    {
        
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        //调用结束后删除
        TraceIdUtil.remove();
    }
}


/**
 * 此处也可以继承WebMvcConfigurationSupport
 */
@Configuration
public class WebConfigurer implements WebMvcConfigurer {
 
    @Resource
    private LogInterceptor logInterceptor;
 
    /**
     * 添加拦截规则
     * @param registry
     */
    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        registry.addInterceptor(logInterceptor)
                 //所有的请求都要拦截。
                .addPathPatterns("/**");
    }
}

工具类

public class TraceIdUtil
{
  public static final String TRACE_ID = "requestId";
    
  public static String getTraceId()
  {
     String traceId =(String) MDC.get(TRACE_ID);
     return traceId == null ? "" : traceId;
  }
  
  public static void setTraceId(String traceId)
  {
      MDC.put(TRACE_ID,traceId);
  }
  
  public static void remove()
  {
      MDC.remove(TRACE_ID);
      
  }
  
  public static void clear()
  {
      MDC.clear();
  }
  
  public static String generateTraceId() {
     return UUID.randomUUID().toString().replace("-", "");
  }

日志文件配置

1	<property name="LOG_PATTERN" value="%date{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level [%X{requestId}] %logger{36} - %msg%n" />

重点是%X{requestId},requestId和MDC中的键名称保持一致。

MDC 存在的问题

至此基本的功能已经实现，但是存在一下几个问题

多线程情况下，子线程中打印日志会丢失traceId.
HTTP跨服务之间的调用丢失traceId.

子线程日志打印丢失traceId

问题重现

@LogAnnotation(model="用户管理",func="查询用户信息",desc="根据用户名称")
  @GetMapping("getUserByName")
  public Result getUserByName(@RequestParam String name)
  {
      //主线程日志
      logger.info("getUserByName paramter name:"+name);
      for(int i=0;i<5;i++)
      {
         //子线程日志
          threadPoolTaskExecutor.execute(()->{
              logger.info("child thread:{}",name);
              userService.getUserByName(name); 
          });
      }
      
      return Result.success();
  }

运行结果

1
2
3

2022-03-13 12:45:44.156 [http-nio-8089-exec-1] INFO  [ec05a600ed1a4556934a3afa4883766a] c.s.fw.controller.UserController - getUserByName paramter name:1
2022-03-13 12:45:44.173 [Pool-A1] INFO  [] c.s.fw.controller.UserController - child thread:1

从运行的结果来看，子线程打印日志，日志中的traceId信息已经丢失。

解决方案

子线程在打印日志的过程中traceId将丢失，解决方案为重写线程池(对于直接new Thread 创建线程的情况不考略),实际开发中也需要禁止这种情况。

public class ThreadPoolExecutorMdcWrapper extends ThreadPoolTaskExecutor
{
    private static final long serialVersionUID = 3940722618853093830L;

    @Override
    public void execute(Runnable task)
    {
        super.execute(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
    }

    @Override
    public <T> Future<T> submit(Callable<T> task)
    {
        return super
                .submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
    }

    @Override
    public Future<?> submit(Runnable task)
    {
        return super
                .submit(ThreadMdcUtil.wrap(task, MDC.getCopyOfContextMap()));
    }
}

因为Spring Boot ThreadPoolTaskExecutor 已经对ThreadPoolExecutor进行封装，只需要继承ThreadPoolTaskExecutor重写相关的执行方法即可。

public class ThreadMdcUtil
{
    public static void setTraceIdIfAbsent() {
        if (MDC.get(TraceIdUtil.TRACE_ID) == null) 
        {
            MDC.put(TraceIdUtil.TRACE_ID, TraceIdUtil.generateTraceId());
        }
    }

    public static <T> Callable<T> wrap(final Callable<T> callable, final Map<String, String> context) {
        return () -> {
            if (context == null) {
                MDC.clear();
            } else {
                MDC.setContextMap(context);
            }
            setTraceIdIfAbsent();
            try {
                return callable.call();
            } finally {
                MDC.clear();
            }
        };
    }

    public static Runnable wrap(final Runnable runnable, final Map<String, String> context) {
        return () -> {
            if (context == null) {
                MDC.clear();
            } else {
                MDC.setContextMap(context);
            }
            //设置traceId
            setTraceIdIfAbsent();
            try {
                runnable.run();
            } finally {
                MDC.clear();
            }
        };
    }
}

代码说明：

判断当前线程对应MDC的Map是否存在，如果存在则设置
设置MDC中的traceId值，不存在则新生成，如果是子线程，MDC中traceId不为null
执行run方法

线程池配置

@Configuration
public class ThreadPoolTaskExecutorConfig
{
    //最大可用的CPU核数
    public static final int PROCESSORS = Runtime.getRuntime().availableProcessors();
    
    @Bean
    public ThreadPoolExecutorMdcWrapper getExecutor()
    {
        ThreadPoolExecutorMdcWrapper executor =new ThreadPoolExecutorMdcWrapper();
        executor.setCorePoolSize(PROCESSORS *2);
        executor.setMaxPoolSize(PROCESSORS * 4);
        executor.setQueueCapacity(50);
        executor.setKeepAliveSeconds(60);
        executor.setThreadNamePrefix("Task-A");
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
        executor.initialize();
        return executor;
    }
}

重新运行结果发现子线程能够正常获取traceid信息进行跟踪。

1
2
3

2022-03-13 13:19:30.688 [Task-A1] INFO  [482929425cbc4476a4e7168615af7890] c.s.fw.controller.UserController - child thread:1
2022-03-13 13:19:31.003 [Task-A1] INFO  [482929425cbc4476a4e7168615af7890] c.s.fw.service.impl.UserServiceImpl - name:1

HTTP调用丢失traceId

HTTP调用第三方服务接口时traceId丢失，需要在发送请求时在Request Header中添加traceId，在被调用方添加拦截器获取header中的traceId添加到MDC中。

HTTP调用有多种方式，比较常见的有HttpClient、OKHttp、RestTemplate，以RestTemplate调用为例。

接口调用方

public class RestTemplateTraceIdInterceptor implements
        ClientHttpRequestInterceptor
{
    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body,
            ClientHttpRequestExecution clientHttpRequestExecution) throws IOException
    {
        String traceId=MDC.get("requestId");
        if(traceId!=null)
        {
            request.getHeaders().set("requestId", traceId);
        }
        else
        {
            request.getHeaders().set("requestId", UUID.randomUUID().toString().replace("-", ""));
        }
        return clientHttpRequestExecution.execute(request, body);
    }

}

RestTemplate添加拦截器即可。

1 2	restTemplate.setInterceptors(Arrays.asList(new RestTemplateTraceIdInterceptor()));

第三方服务需要添加拦截器

@Component
public class LogInterceptor implements HandlerInterceptor
{
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //如果有上层调用就用上层的ID
        String traceId = request.getHeader(TraceIdUtil.TRACE_ID);
        if (StringUtil.isEmpty(traceId)) 
        {
            TraceIdUtil.setTraceId(TraceIdUtil.generateTraceId());
        }
        else
        {
            TraceIdUtil.setTraceId(traceId);
        }
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
            throws Exception 
    {
        
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
            throws Exception {
        //调用结束后删除
        TraceIdUtil.remove();
    }
}