SpringBoot+MDC实现全链路调用日志跟踪,排查问题更方便

写在前面

通过本文将了解到什么是MDC、MDC应用中存在的问题、如何解决存在的问题

MDC介绍

简介:

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。MDC 的内容则由程序在适当的时候保存进去。对于一个 Web 应用来说,通常是在请求被处理的最开始保存这些数据

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
优点:
  • 代码简洁,日志风格统一,不需要在log打印中手动拼写traceId,即LOGGER.info("traceId:{} ", traceId)

暂时只能想到这一点

MDC使用

  • 添加拦截器
    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(Constants.TRACE_ID);
            if (traceId == null) {
                traceId = TraceIdUtil.getTraceId();
            }

            MDC.put(Constants.TRACE_ID, 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
            MDC.remove(Constants.TRACE_ID);
        }
    }
  • 修改日志格式
[TRACEID:%X{traceId}] %d{HH:mm:ss.SSS} %-5level %class{-1}.%M()/%L - %msg%xEx%n

重点是%X{traceId},traceId和MDC中的键名称一致
简单使用就这么容易,但是在有些情况下traceId将获取不到

MDC 存在的问题

  • 子线程中打印日志丢失traceId

  • HTTP调用丢失traceId

    ......丢失traceId的情况,来一个再解决一个,绝不提前优化

解决MDC存在的问题

子线程日志打印丢失traceId

子线程在打印日志的过程中traceId将丢失,解决方式为重写线程池,对于直接new创建线程的情况不考略【实际应用中应该避免这种用法】,重写线程池无非是对任务进行一次封装

  • 线程池封装类:ThreadPoolExecutorMdcWrapper.java
public class ThreadPoolExecutorMdcWrapper extends ThreadPoolExecutor {
     public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
                                         BlockingQueue workQueue) {
         super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
     }

     public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
                                         BlockingQueue workQueue, ThreadFactory threadFactory) {
         super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory);
     }

     public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
                                         BlockingQueue workQueue, RejectedExecutionHandler handler) {
         super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);
     }

     public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit,
                                         BlockingQueue workQueue, ThreadFactory threadFactory,
                                         RejectedExecutionHandler handler) {
         super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);
     }

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

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

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

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

说明:

  • 继承ThreadPoolExecutor类,重新执行任务的方法
  • 通过ThreadMdcUtil对任务进行一次包装
  • 线程traceId封装工具类:ThreadMdcUtil.java
public class ThreadMdcUtil {
        public static void setTraceIdIfAbsent() {
            if (MDC.get(Constants.TRACE_ID) == null) {
                MDC.put(Constants.TRACE_ID, TraceIdUtil.getTraceId());
            }
        }

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

说明【以封装Runnable为例】:

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

代码等同于以下写法,会更直观

public static Runnable wrap(final Runnable runnable, final Map context) {
        return new Runnable() {
            @Override
            public void run() {
                if (context == null) {
                    MDC.clear();
                } else {
                    MDC.setContextMap(context);
                }
                setTraceIdIfAbsent();
                try {
                    runnable.run();
                } finally {
                    MDC.clear();
                }
            }
        };
    }

重新返回的是包装后的Runnable,在该任务执行之前【runnable.run()】先将主线程的Map设置到当前线程中【 即MDC.setContextMap(context)】,这样子线程和主线程MDC对应的Map就是一样的了

HTTP调用丢失traceId

在使用HTTP调用第三方服务接口时traceId将丢失,需要对HTTP调用工具进行改造,在发送时在request header中添加traceId,在下层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,所以只给出这几种HTTP调用的解决方式

HttpClient:

  • 实现HttpClient拦截器
public class HttpClientTraceIdInterceptor implements HttpRequestInterceptor {
        @Override
        public void process(HttpRequest httpRequest, HttpContext httpContext) throws HttpException, IOException {
            String traceId = MDC.get(Constants.TRACE_ID);
            //当前线程调用中有traceId,则将该traceId进行透传
            if (traceId != null) {
                //添加请求体
                httpRequest.addHeader(Constants.TRACE_ID, traceId);
            }
        }
    }

实现HttpRequestInterceptor接口并重写process方法

如果调用线程中含有traceId,则需要将获取到的traceId通过request中的header向下透传下去

  • 为HttpClient添加拦截器
private static CloseableHttpClient httpClient = HttpClientBuilder.create()
                .addInterceptorFirst(new HttpClientTraceIdInterceptor())
                .build();

通过addInterceptorFirst方法为HttpClient添加拦截器

OKHttp:

  • 实现OKHttp拦截器
public class OkHttpTraceIdInterceptor implements Interceptor {
     @Override
     public Response intercept(Chain chain) throws IOException {
         String traceId = MDC.get(Constants.TRACE_ID);
         Request request = null;
         if (traceId != null) {
             //添加请求体
             request = chain.request().newBuilder().addHeader(Constants.TRACE_ID, traceId).build();
         }
         Response originResponse = chain.proceed(request);

         return originResponse;
     }
 }
实现Interceptor拦截器,重写interceptor方法,实现逻辑和HttpClient差不多,如果能够获取到当前线程的traceId则向下透传
  • 为OkHttp添加拦截器
    private static OkHttpClient client = new OkHttpClient.Builder()
               .addNetworkInterceptor(new OkHttpTraceIdInterceptor())
               .build();
调用addNetworkInterceptor方法添加拦截器

RestTemplate:

  • 实现RestTemplate拦截器
    public class RestTemplateTraceIdInterceptor implements ClientHttpRequestInterceptor {
        @Override
        public ClientHttpResponse intercept(HttpRequest httpRequest, byte[] bytes, ClientHttpRequestExecution clientHttpRequestExecution) throws IOException {
            String traceId = MDC.get(Constants.TRACE_ID);
            if (traceId != null) {
                httpRequest.getHeaders().add(Constants.TRACE_ID, traceId);
            }

            return clientHttpRequestExecution.execute(httpRequest, bytes);
        }
    }
实现ClientHttpRequestInterceptor接口,并重写intercept方法,其余逻辑都是一样的不重复说明
  • 为RestTemplate添加拦截器
restTemplate.setInterceptors(Arrays.asList(new RestTemplateTraceIdInterceptor()));
调用setInterceptors方法添加拦截器

第三方服务拦截器:

HTTP调用第三方服务接口全流程traceId需要第三方服务配合,第三方服务需要添加拦截器拿到request header中的traceId并添加到MDC中

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(Constants.TRACE_ID);
        if (traceId == null) {
            traceId = TraceIdUtils.getTraceId();
        }

        MDC.put("traceId", 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 {
        MDC.remove(Constants.TRACE_ID);
    }
}

说明:

  • 先从request header中获取traceId
  • 从request header中获取不到traceId则说明不是第三方调用,直接生成一个新的traceId
  • 将生成的traceId存入MDC中

除了需要添加拦截器之外,还需要在日志格式中添加traceId的打印,如下:

[TRACEID:%X{traceId}] %d{HH:mm:ss.SSS} %-5level %class{-1}.%M()/%L - %msg%xEx%n

需要添加%X{traceId}

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