SpringBoot + MDC 实现全链路调用日志跟踪-526互联

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)
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

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

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

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 <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);
            }
            setTraceIdIfAbsent();
            try {
                runnable.run();
            } finally {
                MDC.clear();
            }
        };
    }
}