Log4j2报错ERROR StatusLogger Unrecognized format specifier

问题

使用maven-shade-plugin或者maven-assembly-plugin插件把项目打成一个可执行JAR包时，如果你引入了log4j2会出现如下问题：

ERROR StatusLogger Unrecognized format specifier [d]
ERROR StatusLogger Unrecognized conversion specifier [d] starting at position 16 in conversion pattern.
ERROR StatusLogger Unrecognized format specifier [thread]
ERROR StatusLogger Unrecognized conversion specifier [thread] starting at position 25 in conversion pattern.
ERROR StatusLogger Unrecognized format specifier [level]
ERROR StatusLogger Unrecognized conversion specifier [level] starting at position 35 in conversion pattern.
ERROR StatusLogger Unrecognized format specifier [logger]
ERROR StatusLogger Unrecognized conversion specifier [logger] starting at position 47 in conversion pattern.
ERROR StatusLogger Unrecognized format specifier [msg]
ERROR StatusLogger Unrecognized conversion specifier [msg] starting at position 54 in conversion pattern.
ERROR StatusLogger Unrecognized format specifier [n]
ERROR StatusLogger Unrecognized conversion specifier [n] starting at position 56 in conversion pattern.

解决方法

pom中添加如下配置。

<plugin>
   <groupId>org.apache.maven.plugins</groupId>
   <artifactId>maven-shade-plugin</artifactId>
   <version>2.4.3</version>
   <executions>
       <execution>
           <phase>package</phase>
           <goals>
               <goal>shade</goal>
           </goals>
           <configuration>
               <filters>
                   <filter>
                       <artifact>*:*</artifact>
                       <excludes>
                           <exclude>META-INF/*.SF</exclude>
                           <exclude>META-INF/*.DSA</exclude>
                           <exclude>META-INF/*.RSA</exclude>
                       </excludes>
                   </filter>
               </filters>
               <finalName>${artifactId}-${env}-${version}</finalName>
               <transformers>
                   <transformer
                           implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                       <mainClass>xxx.yyyy.zzz.Main</mainClass>
                   </transformer>
                   <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
                       <resource>META-INF/spring.handlers</resource>
                   </transformer>
                   <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
                       <resource>META-INF/spring.schemas</resource>
                   </transformer>
                   <transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
                       <resource>META-INF/spring.tooling</resource>
                   </transformer>
                   <transformer
                           implementation="org.apache.maven.plugins.shade.resource.ComponentsXmlResourceTransformer"/>
                   <transformer
                           implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
                   <transformer implementation="com.github.edwgiz.mavenShadePlugin.log4j2CacheTransformer.PluginsCacheFileTransformer" />
               </transformers>
           </configuration>
       </execution>
   </executions>
   <dependencies>
       <dependency>
           <groupId>com.github.edwgiz</groupId>
           <artifactId>maven-shade-plugin.log4j2-cachefile-transformer</artifactId>
           <version>2.6.1</version>
       </dependency>
   </dependencies>
</plugin>

原因分析

log4j2 是采用的插件式编程，当log4j2包编译时，或者含有log4j2插件的包编译时，会将需要加载的插件信息放在META-INF/org/apache/logging/log4j/core/config/plugins/Log4j2Plugins.dat这个文件中（包括官方logj42的原生插件），然后项目启动的时候，log4j2会在各个jar包的META-INF目录下扫描这个插件信息文件，然后去加载插件。

但是当项目被打成一个jar包时，如果两个不同的jar包中都有Log4j2Plugins.dat 这个文件，就会出现问题，其中一个文件会被另一个覆盖，导致项目启动的时候有一个文件中的插件不能被正常加载，导致报错。

解决这个问题就是当所有jar包被打成一个jar包时，需要对各个jar包中的Log4j2Plugins.dat进行合并，这就是maven-shade-plugin.log4j2-cachefile-transformer这个包所做的事情了。