Spring Boot + MDC 實現(xiàn)全鏈路調用日志跟蹤

寫在前面

通過本文將了解到什么是MDC、MDC應用中存在的問題、如何解決存在的問題

MDC介紹

簡介：

MDC（Mapped Diagnostic Context，映射調試上下文）是 log4j 、logback及l(fā)og4j2 提供的一種方便在多線程條件下記錄日志的功能。MDC 可以看成是一個與當前線程綁定的哈希表，可以往其中添加鍵值對。MDC 中包含的內容可以被同一線程中執(zhí)行的代碼所訪問。當前線程的子線程會繼承其父線程中的 MDC 的內容。當需要記錄日志時，只需要從 MDC 中獲取所需的信息即可。MDC 的內容則由程序在適當?shù)臅r候保存進去。對于一個 Web 應用來說，通常是在請求被處理的最開始保存這些數(shù)據(jù)

API說明：

• clear() => 移除所有MDC
• get (String key) => 獲取當前線程MDC中指定key的值
• getContext() => 獲取當前線程MDC的MDC
• put(String key, Object o) => 往當前線程的MDC中存入指定的鍵值對
• remove(String key) => 刪除當前線程MDC中指定的鍵值對

優(yōu)點：

• 代碼簡潔，日志風格統(tǒng)一，不需要在log打印中手動拼寫traceId，即LOGGER.info("traceId:{} ", traceId)

暫時只能想到這一點

MDC使用

• 添加攔截器

??public?class?LogInterceptor?implements?HandlerInterceptor?{
??????@Override
??????public?boolean?preHandle(HttpServletRequest?request,?HttpServletResponse?response,?Object?handler)?throws?Exception?{
??????????//如果有上層調用就用上層的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?{
??????????//調用結束后刪除
??????????MDC.remove(Constants.TRACE_ID);
??????}
}

• 修改日志格式

<property?name="pattern">[TRACEID:%X{traceId}]?%d{HH:mm:ss.SSS}?%-5level?%class{-1}.%M()/%L?-?%msg%xEx%nproperty>

重點是%X{traceId}，traceId和MDC中的鍵名稱一致

簡單使用就這么容易，但是在有些情況下traceId將獲取不到

MDC 存在的問題

• 子線程中打印日志丟失traceId
• HTTP調用丟失traceId

丟失traceId的情況，來一個再解決一個，絕不提前優(yōu)化

解決MDC存在的問題

子線程日志打印丟失traceId

子線程在打印日志的過程中traceId將丟失，解決方式為重寫線程池，對于直接new創(chuàng)建線程的情況不考略【實際應用中應該避免這種用法】，重寫線程池無非是對任務進行一次封裝

• 線程池封裝類：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()));
??????}
}

說明：

• 繼承ThreadPoolExecutor類，重新執(zhí)行任務的方法
• 通過ThreadMdcUtil對任務進行一次包裝
• 線程traceId封裝工具類：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();
??????????????}
??????????};
??????}
}

說明【以封裝Runnable為例】：

• 判斷當前線程對應MDC的Map是否存在，存在則設置
• 設置MDC中的traceId值，不存在則新生成，針對不是子線程的情況，如果是子線程，MDC中traceId不為null
• 執(zhí)行run方法

代碼等同于以下寫法，會更直觀

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();
??????????????????}
??????????????}
??????????};
??????}

重新返回的是包裝后的Runnable，在該任務執(zhí)行之前【runnable.run()】先將主線程的Map設置到當前線程中【 即MDC.setContextMap(context)】，這樣子線程和主線程MDC對應的Map就是一樣的了

HTTP調用丟失traceId

在使用HTTP調用第三方服務接口時traceId將丟失，需要對HTTP調用工具進行改造，在發(fā)送時在request header中添加traceId，在下層被調用方添加攔截器獲取header中的traceId添加到MDC中

HTTP調用有多種方式，比較常見的有HttpClient、OKHttp、RestTemplate，所以只給出這幾種HTTP調用的解決方式

HttpClient：

• 實現(xiàn)HttpClient攔截器

public?class?HttpClientTraceIdInterceptor?implements?HttpRequestInterceptor?{
????@Override
????public?void?process(HttpRequest?httpRequest,?HttpContext?httpContext)?throws?HttpException,?IOException?{
????????String?traceId?=?MDC.get(Constants.TRACE_ID);
????????//當前線程調用中有traceId，則將該traceId進行透傳
????????if?(traceId?!=?null)?{
????????????//添加請求體
????????????httpRequest.addHeader(Constants.TRACE_ID,?traceId);
????????}
????}
}
復制代碼

• 實現(xiàn)HttpRequestInterceptor接口并重寫process方法

• 如果調用線程中含有traceId，則需要將獲取到的traceId通過request中的header向下透傳下去

• 為HttpClient添加攔截器

private?static?CloseableHttpClient?httpClient?=?HttpClientBuilder.create()
??????????????.addInterceptorFirst(new?HttpClientTraceIdInterceptor())

通過addInterceptorFirst方法為HttpClient添加攔截器

OKHttp：

• 實現(xiàn)OKHttp攔截器

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)?{
??????????????//添加請求體
??????????????request?=?chain.request().newBuilder().addHeader(Constants.TRACE_ID,?traceId).build();
??????????}
??????????Response?originResponse?=?chain.proceed(request);
??
??????????return?originResponse;
??????}
}

實現(xiàn)Interceptor攔截器，重寫interceptor方法，實現(xiàn)邏輯和HttpClient差不多，如果能夠獲取到當前線程的traceId則向下透傳

• 為OkHttp添加攔截器

????private?static?OkHttpClient?client?=?new?OkHttpClient.Builder()
??????????????.addNetworkInterceptor(new?OkHttpTraceIdInterceptor())
??????????????.build();

調用addNetworkInterceptor方法添加攔截器

RestTemplate：

• 實現(xiàn)RestTemplate攔截器

??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);
??????}
}

實現(xiàn)ClientHttpRequestInterceptor接口，并重寫intercept方法，其余邏輯都是一樣的不重復說明

• 為RestTemplate添加攔截器

??restTemplate.setInterceptors(Arrays.asList(new?RestTemplateTraceIdInterceptor()));

調用setInterceptors方法添加攔截器

第三方服務攔截器：

HTTP調用第三方服務接口全流程traceId需要第三方服務配合，第三方服務需要添加攔截器拿到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?{
????????//如果有上層調用就用上層的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);
????}
}

說明：

• 先從request header中獲取traceId
• 從request header中獲取不到traceId則說明不是第三方調用，直接生成一個新的traceId
• 將生成的traceId存入MDC中

除了需要添加攔截器之外，還需要在日志格式中添加traceId的打印，如下：

<property?name="pattern">[TRACEID:%X{traceId}]?%d{HH:mm:ss.SSS}?%-5level?%class{-1}.%M()/%L?-?%msg%xEx%nproperty>
復制代碼

需要添加%X{traceId}

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