使用maven构建项目时，如果项目中有log4j的依赖，在运行程序时可能会出现在同一个类中log4j-over-slf4j.jar和 slf4j-log4j12.jar冲突的问题：
项目报错内容为：
Exception in thread "main" java.lang.ExceptionInInitializerError
at org.apache.log4j.LogManager.getLogger(LogManager.java:44)
at org.slf4j.impl.Log4jLoggerFactory.getLogger(Log4jLoggerFactory.java:66)
at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:270)
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:657)
at org.apache.hadoop.conf.Configuration.<clinit>(Configuration.java:173)
Caused by: java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar AND slf4j-log4j12.jar on the class path, preempting StackOverflowError. See also http://www.slf4j.org/codes.html#log4jDelegationLoop for more details.
at org.apache.log4j.Log4jLoggerFactory.<clinit>(Log4jLoggerFactory.java:49)
... 8 more
原因是：log4j-over-slf4j和slf4j-log4j12是跟Java日志系统相关的两个jar包，当它们同时出现在classpath下时，就可能会引起堆栈溢出异常。
解决办法：pom.xml文件中，在使用到的依赖包中添加<exclusion>标签将slf4j-log4j12.jar排除即可：
例如：红色字体是排除的内容
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>2.6.0</version>
<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
</exclusions>
</dependency>