1.概念
MDC（Mapped Diagnostic Context，映射调试上下文）是 log4j 和 logback 提供的一种方便在多线程条件下记录日志的功能，也可以说是一种轻量级的日志跟踪工具。
MDC使用的是ThreadLocal记录数据，把数据和当前线程进行绑定,一次请求进来的所有操作都能看到
2.使用:
在用户请求进来的时候生成当前请求的traceId(使用拦截器在请求进来的时候生成，traceId要唯一)，放到MDC中
拦截器
@Component@Slf4jpublic class MDCInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {String tractId = MDC.get(Constants.TRACE_ID);if (tractId == null) {tractId = TraceIdUtil.getTraceId();}MDC.put(Constants.TRACE_ID, tractId);return true;}@Overridepublic void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);}@Overridepublic void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {MDC.remove(Constants.TRACE_ID);}}
配置拦截器
@Autowiredprivate MDCInterceptor mdcInterceptor;@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(mdcInterceptor).excludePathPatterns("/login");}
2.在日志配置文件中配置打印traceId
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender"><encoder><!--格式化输出：%d表示日期，%thread表示线程名，%-5level：级别从左显示5个字符宽度%msg：日志消息，%n是换行符--><pattern>%d{yyyy-MM-dd HH:mm:ss.SSS} %thread | [%X{traceId}] | %-5level %logger{50} %msg%n</pattern><charset>utf8</charset></encoder></appender>
配置完之后打印一个日志就能看到traceId
3.MDC传递值给子线程
MDC.getCopyOfContextMap() 该方法获取当前线程MDC中的数据，再把获取到的数据放到子线程中即可，项目中我们一般不会直接new一个thread，而是使用线程池，所以这里继承ThreadPoolExecutor重写线程池，在线程池的线程中进行设置
线程池代码
public class ThreadPoolExecutorMdcWrapper extends ThreadPoolExecutor {public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);}public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) {super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory);}public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler) {super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);}public ThreadPoolExecutorMdcWrapper(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) {super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);}@Overridepublic void execute(Runnable runnable) {super.execute(MDCUtil.wrap(runnable,MDC.getCopyOfContextMap()));}@Overridepublic Future<?> submit(Runnable runnable) {return super.submit(MDCUtil.wrap(runnable,MDC.getCopyOfContextMap()));}@Overridepublic <T> Future<T> submit(Runnable runnable, T result) {return super.submit(MDCUtil.wrap(runnable,MDC.getCopyOfContextMap()), result);}@Overridepublic <T> Future<T> submit(Callable<T> callable) {return super.submit(MDCUtil.wrap(callable,MDC.getCopyOfContextMap()));}}
MDC工具类
public class MDCUtil {public static Runnable wrap(final Runnable runnable, final Map<String, String> context) {return () -> {if (context == null) {MDC.clear();}else {MDC.setContextMap(context);}//如果不是子线程的话先生成traceIdsetTraceIdIfAbsent();try {runnable.run();}finally {MDC.clear();}};}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 ((T) callable.call());}finally {MDC.clear();}};}public static void setTraceIdIfAbsent() {if (MDC.get(Constants.TRACE_ID) == null) {MDC.put(Constants.TRACE_ID, TraceIdUtil.getTraceId());}}}
把线程池交给spring管理
@Configurationpublic class BeanConfig {@Beanpublic ThreadPoolExecutorMdcWrapper getThreadPoolExecutorMdcWrapper() {return new ThreadPoolExecutorMdcWrapper(5,10,5,TimeUnit.SECONDS,new LinkedBlockingDeque<>(5));}}
测试
@GetMapping("getIp")public String getIp() {log.info("getIp");threadPoolExecutorMdcWrapper.execute(()->{log.info("子线程 getIp");});return "getIp";}
打印出来的traceId一致
4.使用restTemplate进行http调用MDC传值
restTemplate拦截器
public class RestTemplateTraceIdInterceptor implements ClientHttpRequestInterceptor {@Overridepublic ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {String traceId = MDC.get(Constants.TRACE_ID);if (traceId != null) {request.getHeaders().add(Constants.TRACE_ID, traceId);}return execution.execute(request, body);}}
配置拦截器
@Beanpublic RestTemplate restTemplate( ) {RestTemplateBuilder restTemplateBuilder = new RestTemplateBuilder();RestTemplate restTemplate = restTemplateBuilder.build();//设置Resttemplate的拦截器restTemplate.setInterceptors(Collections.singletonList(new RestTemplateTraceIdInterceptor()));return restTemplate;}
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