Java学习-051-Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the class path, preempting StackOverflowError

错误信息：Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the class path, preempting StackOverflowError

场景：

产品服务器采用spring-boot框架开发，zookeeper作为微服务框架，打包完成后发现服务无法启动，tomcat启动错误日志显示如下所示：

日志文本详情：

 08-Nov-2017 11:32:10.984 INFO [localhost-startStop-1] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
 SLF4J: Class path contains multiple SLF4J bindings.
 SLF4J: Found binding in [jar:file:/shenmajr/shenma-frss-web/webapps/ROOT/WEB-INF/lib/slf4j-log4j12-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
 SLF4J: Found binding in [jar:file:/shenmajr/shenma-frss-web/webapps/ROOT/WEB-INF/lib/logback-classic-1.1.11.jar!/org/slf4j/impl/StaticLoggerBinder.class]
 SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
 SLF4J: Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the class path, preempting StackOverflowError.
 SLF4J: See also http://www.slf4j.org/codes.html#log4jDelegationLoop for more details.
 08-Nov-2017 11:32:11.129 SEVERE [localhost-startStop-1] org.apache.catalina.core.ContainerBase.addChildInternal ContainerBase.addChild: start:
  org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[]]
     at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:153)
     at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
     at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
     at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
     at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:940)
     at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1816)
     at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
     at java.lang.Thread.run(Thread.java:745)
 Caused by: java.lang.ExceptionInInitializerError
     at org.slf4j.impl.StaticLoggerBinder.<init>(StaticLoggerBinder.java:72)
     at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:45)
     at org.slf4j.LoggerFactory.bind(LoggerFactory.java:150)
     at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:124)
     at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:412)
     at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:357)
     at org.apache.commons.logging.impl.SLF4JLogFactory.getInstance(SLF4JLogFactory.java:155)
     at org.apache.commons.logging.impl.SLF4JLogFactory.getInstance(SLF4JLogFactory.java:132)
     at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:273)
     at org.springframework.boot.web.support.SpringBootServletInitializer.onStartup(SpringBootServletInitializer.java:85)
     at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:169)
     at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5292)
     at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
     ... 10 more
 Caused by: java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the class path, preempting StackOverflowError. See also http://www.slf4j.org/codes.html#log4jDelegationLoop for more details.
     at org.slf4j.impl.Log4jLoggerFactory.<clinit>(Log4jLoggerFactory.java:54)
     ... 23 more

解决方法如下所示：

类库冲突是因为tomcat在启动加载类库时，加载类引起的。通过mvn dependency:tree命令查看maven项目工程类库的依赖关系，可以发现如下均有引用slf4j-log4j12的类库，因而在项目工程中将此引用依赖通过exclusions取消即可。

(⊙o⊙)…，上图中红框错位了，大家勿怪哈

实际项目中，可能存在各种各样的冲突，但只要稍用心排查一下冲突的依赖，解决此类问题还是比较容易的。