spring boot 启动报错：

Caused by: java.lang.IllegalArgumentException: LoggerFactory is not a Logback LoggerContext but Logback is on the classpath. Either remove Logback or the competing implementation (class org.slf4j.impl.Log4jLoggerFactory loaded from file:/usr/local/tomcat/webapps/app/WEB-INF/lib/slf4j-log4j12-1.7.25.jar). If you are using WebLogic you will need to add 'org.slf4j' to prefer-application-packages in WEB-INF/weblogic.xml: org.slf4j.impl.Log4jLoggerFactory        at org.springframework.util.Assert.instanceCheckFailed(Assert.java:655)        at org.springframework.util.Assert.isInstanceOf(Assert.java:555)        at org.springframework.boot.logging.logback.LogbackLoggingSystem.getLoggerContext(LogbackLoggingSystem.java:286)        at org.springframework.boot.logging.logback.LogbackLoggingSystem.beforeInitialize(LogbackLoggingSystem.java:102)        at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationStartingEvent(LoggingApplicationListener.java:220)        at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:199)        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:69)        at org.springframework.boot.SpringApplicationRunListeners.starting(SpringApplicationRunListeners.java:48)        at org.springframework.boot.SpringApplication.run(SpringApplication.java:302)        at org.springframework.boot.web.servlet.support.SpringBootServletInitializer.run(SpringBootServletInitializer.java:157)        at org.springframework.boot.web.servlet.support.SpringBootServletInitializer.createRootApplicationContext(SpringBootServletInitializer.java:137)        at org.springframework.boot.web.servlet.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:91)        at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:171)        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5139)        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)        ... 26 more

出现这个问题通常的原因工程中使用了多个开源jar，每个开源jar都有自己的日志实现方式，比如slf+log4j,slf+logback等，其中slf是一个抽象接口，有很多种实现，但是工程中只能有一种，解决方法在异常中已经提示出来：

Either remove Logback or the competing implementation (class org.slf4j.impl.Log4jLoggerFactory loaded from file:/usr/local/tomcat/webapps/app/WEB-INF/lib/slf4j-log4j12-1.7.25.jar).

需要在logback和slf-log4j之间去掉一个，其中spring boot用的是logback，可以去掉slf-log4j；

通过

mvn dependency:tree

可以看到那些jar中依赖了slf-log4j，然后修改pom，将其排除掉

                 
      
       org.apache.hadoop
                  
      
       hadoop-client
                  
      
       2.6.5
                  
                      
                           
        
         org.slf4j
                            
        
         slf4j-log4j12
                        
                   
              
     

然后打包即可；