一例由slf4j與log4j版本不兼容引發的ClassNotFoundException

錯誤描述：

Failed to instantiate SLF4J LoggerFactory
Reported exception:
java.lang.NoClassDefFoundError: org/apache/log4j/Level
	at org.slf4j.LoggerFactory.bind(LoggerFactory.java:128)
	at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:108)
	at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:279)
	at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:252)
	at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:265)
	at org.apache.zookeeper.server.quorum.QuorumPeerMain.<clinit>(QuorumPeerMain.java:64)
	at org.apache.curator.test.TestingServer.<init>(TestingServer.java:74)
	at org.apache.curator.test.TestingServer.<init>(TestingServer.java:68)
	at org.apache.curator.test.TestingServer.<init>(TestingServer.java:45)
	at cache.PathCacheExample.main(PathCacheExample.java:50)
Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Level
	at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 10 more

解決方案：

pom.xml中增長如下配置，以強制替換原有版本的slf4j和log4j的artifact：

<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.5</version>
</dependency>
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.5</version>
</dependency>
<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>