(七)Logback中的MDC(Mapped Diagnostic Context)

待我称王封你为后i 2022-02-03 23:55 231阅读 0赞

一、为什么会有MDC(MappedDiagnosticContext)?

审计和调试分布式应用是logback的设计目标之一，在多线程环境中，不同的线程会处理不同的客户端，为了区分不同客户端日志输出，一种轻量级但不可取的做法是为每个实例化一个新的、完全分离日志记录器，这种方法会产生很多的日志记录器而且难以管理。

更轻量级的做法是唯一标记每个来自客户端的日志请求，为了唯一标记每个请求，用户把上下文信息放置到MDC中，MDC类的核心方法如下，完整方法参考[MDC javadocs][]。

package org.slf4j;
    
    public class MDC {
      //Put a context value as identified by key
      //into the current thread's context map.
      public static void put(String key, String val);
    
      //Get the context identified by the key parameter.
      public static String get(String key);
    
      //Remove the context identified by the key parameter.
      public static void remove(String key);
    
      //Clear all entries in the MDC.
      public static void clear();
    }

1、基本MDC的使用

package chapters.mdc;
    
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.slf4j.MDC;
    
    import ch.qos.logback.classic.PatternLayout;
    import ch.qos.logback.core.ConsoleAppender;
    
    public class SimpleMDC {
      static public void main(String[] args) throws Exception {
    
        // You can put values in the MDC at any time. Before anything else
        // we put the first name
        MDC.put("first", "Dorothy");
    
        
        Logger logger = LoggerFactory.getLogger(SimpleMDC.class);
        // We now put the last name
        MDC.put("last", "Parker");
    
        // The most beautiful two words in the English language according
        // to Dorothy Parker:
        logger.info("Check enclosed.");
        logger.debug("The most beautiful two words in English.");
    
        MDC.put("first", "Richard");
        MDC.put("last", "Nixon");
        logger.info("I am not a crook.");
        logger.info("Attributed to the former US president. 17 Nov 1973.");
      }
    
    }

logback配置文件如下：

<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender"> 
      <layout>
        <Pattern>%X{first} %X{last} - %m%n</Pattern>
      </layout> 
    </appender>

注意：通过%X转换词可以获取MDC设置的变量值。

日志输出如下：

Dorothy Parker - Check enclosed.
    Dorothy Parker - The most beautiful two words in English.
    Richard Nixon - I am not a crook.
    Richard Nixon - Attributed to the former US president. 17 Nov 1973.

[MDC javadocs]: https://www.slf4j.org/api/org/slf4j/MDC.html