MDC搭配ttl使用！！！

本文主要是介绍MDC搭配ttl使用！！！，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

一、简介

MDC 介绍 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。MDC 可以看成是一个与当前线程绑定的Map，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。简而言之，MDC就是日志框架提供的一个InheritableThreadLocal，项目代码中可以将键值对放入其中，然后使用指定方式取出打印即可。

原理：当请求来时生成一个traceId放在InheritableThreadLocal里，然后打印时去取就行了。但在不改动原有输出语句的前提下自然需要日志框架的支持了。

二、使用

2.1配置TraceId 过滤器

package com.by.config;import cn.hutool.core.util.IdUtil;
import org.slf4j.MDC;
import org.springframework.core.annotation.Order;
import org.springframework.util.StringUtils;import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;@Order(1)@WebFilter(urlPatterns = "/*",filterName = "traceIdFilter")
public class TraceIdFilter implements Filter {public final static String MDC_TRACE_ID = "traceId";@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {HttpServletRequest httpRequest = (HttpServletRequest) request;String traceId = httpRequest.getHeader(MDC_TRACE_ID);if (StringUtils.isEmpty(traceId)) {traceId = IdUtil.fastSimpleUUID();;}MDC.put(MDC_TRACE_ID, traceId);chain.doFilter(request, response);}
}

2.2 启动类开启

@SpringBootApplication@ServletComponentScan
public class OpenApp {public static void main(String[] args) {SpringApplication.run(OpenApp.class, args);}}

2.3 配置文件配置日志输出格式

# Spring Boot 日志配置
logging:# 控制台日志输出格式pattern:console: "%d{yyyy-MM-dd HH:mm:ss.SSS} %clr(%-5level) %clr([%X{traceId}]) %clr(${PID:-}) --- %clr(%logger{50}) - %m%n"# 注释说明：
# %d{yyyy-MM-dd HH:mm:ss.SSS}: 时间戳，格式为年-月-日 时:分:秒:毫秒
# %-5level: 日志级别，左对齐且至少占用5个字符宽度
# %clr(...): 使用颜色编码（如果支持）
# [%X{traceId}]: Mapped Diagnostic Context中的traceId，用于记录跟踪请求的唯一标识
# ${PID:-}: 当前进程ID，如果没有则显示空字符串
# ---: 分隔符
# %logger{50}: 日志器名称，最多显示50个字符
# %m: 日志消息内容
# %n: 换行符

三、结果显示

主线程已经得到了我们想要的结果：

那如果我们new一个子线程结果会怎样呢？？

子线程并没有得到我们想要的结果，那怎么解决呢？？？

四、TransmittableThreadLocal实现链路追踪

4.1引入依赖

<dependency><groupId>com.alibaba</groupId><artifactId>transmittable-thread-local</artifactId><version>2.11.5</version><scope>compile</scope></dependency>

4.2、重写{LogbackMDCAdapter}类

注意：要在org.slf4j包下写才可以。

package org.slf4j;import ch.qos.logback.classic.util.LogbackMDCAdapter;
import org.slf4j.spi.MDCAdapter;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;/*** 描述：* 重写{@link LogbackMDCAdapter}类，搭配TransmittableThreadLocal实现父子线程之间的数据传递* 内容直接从{@link LogbackMDCAdapter}类中copy。把copyOnThreadLocal实例化对象更改为TransmittableThreadLocal即可*/
public class TtlMDCAdapter implements MDCAdapter {final ThreadLocal<Map<String, String>> copyOnThreadLocal = new InheritableThreadLocal();private static final int WRITE_OPERATION = 1;private static final int MAP_COPY_OPERATION = 2;final ThreadLocal<Integer> lastOperation = new ThreadLocal();private static TtlMDCAdapter mtcMDCAdapter;static {mtcMDCAdapter = new TtlMDCAdapter();MDC.mdcAdapter = mtcMDCAdapter;}public TtlMDCAdapter() {}public static MDCAdapter getInstance() {return mtcMDCAdapter;}private Integer getAndSetLastOperation(int op) {Integer lastOp = (Integer)this.lastOperation.get();this.lastOperation.set(op);return lastOp;}private boolean wasLastOpReadOrNull(Integer lastOp) {return lastOp == null || lastOp == MAP_COPY_OPERATION;}private Map<String, String> duplicateAndInsertNewMap(Map<String, String> oldMap) {Map<String, String> newMap = Collections.synchronizedMap(new HashMap());if (oldMap != null) {synchronized(oldMap) {newMap.putAll(oldMap);}}this.copyOnThreadLocal.set(newMap);return newMap;}public void put(String key, String val) throws IllegalArgumentException {if (key == null) {throw new IllegalArgumentException("key cannot be null");} else {Map<String, String> oldMap = (Map)this.copyOnThreadLocal.get();Integer lastOp = this.getAndSetLastOperation(WRITE_OPERATION);if (!this.wasLastOpReadOrNull(lastOp) && oldMap != null) {oldMap.put(key, val);} else {Map<String, String> newMap = this.duplicateAndInsertNewMap(oldMap);newMap.put(key, val);}}}public void remove(String key) {if (key != null) {Map<String, String> oldMap = (Map)this.copyOnThreadLocal.get();if (oldMap != null) {Integer lastOp = this.getAndSetLastOperation(WRITE_OPERATION);if (this.wasLastOpReadOrNull(lastOp)) {Map<String, String> newMap = this.duplicateAndInsertNewMap(oldMap);newMap.remove(key);} else {oldMap.remove(key);}}}}public void clear() {this.lastOperation.set(WRITE_OPERATION);this.copyOnThreadLocal.remove();}public String get(String key) {Map<String, String> map = (Map)this.copyOnThreadLocal.get();return map != null && key != null ? (String)map.get(key) : null;}public Map<String, String> getPropertyMap() {this.lastOperation.set(MAP_COPY_OPERATION);return (Map)this.copyOnThreadLocal.get();}public Set<String> getKeys() {Map<String, String> map = this.getPropertyMap();return map != null ? map.keySet() : null;}public Map<String, String> getCopyOfContextMap() {Map<String, String> hashMap = copyOnThreadLocal.get();return hashMap == null ? null : new HashMap(hashMap);}public void setContextMap(Map<String, String> contextMap) {this.lastOperation.set(WRITE_OPERATION);Map<String, String> newMap = Collections.synchronizedMap(new HashMap());newMap.putAll(contextMap);this.copyOnThreadLocal.set(newMap);}
}

4.3、更改spring.factories

在resource/META-INF/spring.factories中进行配置。

org.springframework.context.ApplicationContextInitializer=\
com.jarvan.demo.config.TtlMDCAdapterInitializer

4.4、TtlMDCAdapterInitializer类如下

package com.by.config;import org.slf4j.TtlMDCAdapter;
import org.springframework.context.ApplicationContextInitializer;
import org.springframework.context.ConfigurableApplicationContext;public class TtlMDCAdapterInitializer implements ApplicationContextInitializer {@Overridepublic void initialize(ConfigurableApplicationContext configurableApplicationContext) {TtlMDCAdapter.getInstance();}
}