SpringBoot整合log4j2导入新的依赖出现jar冲突解决

1、问题复现：

之前在SpringBoot中配置整合了log4j2，今天在pom文件中，导入新的依赖(依赖如下)之后，

<dependency>
   <groupId>com.github.tobato</groupId>
   <artifactId>fastdfs-client</artifactId>
   <version>1.26.7</version>
</dependency>   

重启SpringBoot项目时，出现如下错误：

Exception in thread "main" java.lang.IllegalArgumentException: LoggerFactory is not a Logback LoggerContext but Logback is on the classpath. Either remove Logback or the competing implementation (class org.apache.logging.slf4j.Log4jLoggerFactory loaded from file:/D:/00_Develop_Install/Maven/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.12.1/log4j-slf4j-impl-2.12.1.jar). If you are using WebLogic you will need to add 'org.slf4j' to prefer-application-packages in WEB-INF/weblogic.xml: org.apache.logging.slf4j.Log4jLoggerFactory
    at org.springframework.util.Assert.instanceCheckFailed(Assert.java:696)
    at org.springframework.util.Assert.isInstanceOf(Assert.java:596)
    at org.springframework.boot.logging.logback.LogbackLoggingSystem.getLoggerContext(LogbackLoggingSystem.java:281)
    at org.springframework.boot.logging.logback.LogbackLoggingSystem.beforeInitialize(LogbackLoggingSystem.java:104)
    at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationStartingEvent(LoggingApplicationListener.java:239)
    at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:220)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)
    at org.springframework.boot.context.event.EventPublishingRunListener.starting(EventPublishingRunListener.java:70)
    at org.springframework.boot.SpringApplicationRunListeners.starting(SpringApplicationRunListeners.java:47)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:305)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
    at com.pactera.attd.AttdApplication.main(AttdApplication.java:12)

在网上查找相关资料，大部分都是说要 排除SpringBoot默认的logback依赖，但是这个问题，我在整合时，已经去除掉了，所以，很显然不是这个问题。后来，看来篇文章说是，pom文件依赖中的顺序问题，后来就调整了一下顺序，然后重启，报了以下错误(报错信息太多，这里只截取了主要部分)。

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/D:/00_Develop_Install/Maven/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/00_Develop_Install/Maven/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.12.1/log4j-slf4j-impl-2.12.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [ch.qos.logback.classic.util.ContextSelectorStaticBinder]
Logging system failed to initialize using configuration from 'classpath:log4j2.xml'
...

2、问题解决

仔细查看了这次报错的信息，大致意思是说，日志系统出现了多jar包冲突，由于我使用的是log4j2，结果显示还有一个logback的jar包，于是顺着这个问题，查看了一下项目所引jar包，发现了多了以下红框中所展示的jar包，将所引入坐标注释掉，此jar包则没有了，如下图所示。

引入坐标后：

注释坐标后：

 

这下，很明显就知道了原因，也就是说，自己新导入的pom坐标，并未将此jar包排除掉，导致出现了多jar包，既然这样，看来跟新引入的pom坐标的顺序也没关系了，只需要将原先的logback-classic排除掉即可，于是，就在引入的pom坐标下添加了如下排除的依赖。

<exclusions>
     <exclusion>
           <groupId>ch.qos.logback</groupId>
           <artifactId>logback-classic</artifactId>
     </exclusion>
</exclusions>

前后依赖对比，如图。

解决前：

 解决后：

注意：groupId和artifactId一定要写正确，并对应的依赖里面。

然后，重新build项目，发现冲突的jar包，没有了，之后重启SpringBootApplication，项目正常启动，问题解决。