Maven: NoClassDefFoundError, dependency from other imported project conflicting my dependency - maven

Question

I included my library (mylib) as a maven dependency and from then on, this is thrown at runtime:
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/logging/log4j/LogManager
at ...
Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.LogManager
at ...
... 6 more
I tried to exclude the log4j dependency from mylib import, but no change happened.
Excerpt from my pom.xml.
</properties>
<slf4j.version>1.7.7</slf4j.version>
<log4j.version>1.2.17</log4j.version>
<mylib.version>1.0.0</mylib.version>
</properties>
<dependencies>
<dependency>
<groupId>cz.mylib.name</groupId>
<artifactId>mylib</artifactId>
<version>${mylib.version}</version>
<exclusions>
<exclusion>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>${slf4j.version}</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>${slf4j.version}</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>${slf4j.version}</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>${log4j.version}</version>
</dependency>
</dependencies>
Output from mvn dependency:tree
[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) # name ---
[INFO] cz.project.name.name:name:jar:1.30.0
[INFO] +- com.github.cverges.expect4j:expect4j:jar:1.6:compile
[INFO] | +- org.apache.servicemix.bundles:org.apache.servicemix.bundles.oro:jar:2.0.8_6:compile
[INFO] | +- com.jcraft:jsch:jar:0.1.50:compile
[INFO] | +- commons-net:commons-net:jar:3.3:compile
[INFO] | \- net.sourceforge.tcljava:com.springsource.tcl.lang.jacl:jar:1.4.1:compile
[INFO] | \- net.sourceforge.tcljava:com.springsource.tcl.lang:jar:1.4.1:compile
[INFO] +- commons-cli:commons-cli:jar:1.2:compile
[INFO] +- org.apache.commons:commons-exec:jar:1.3:compile
[INFO] +- commons-io:commons-io:jar:2.4:compile
[INFO] +- commons-lang:commons-lang:jar:2.6:compile
[INFO] +- cz.mylib.name:mylib:jar:1.0.0:compile
[INFO] | +- org.apache.logging.log4j:log4j-api:jar:2.11.2:compile
[INFO] | +- javax.xml.bind:jaxb-api:jar:2.3.1:compile
[INFO] | | \- javax.activation:javax.activation-api:jar:1.2.0:compile
[INFO] | \- com.opencsv:opencsv:jar:4.6:compile
[INFO] | +- org.apache.commons:commons-lang3:jar:3.8.1:compile
[INFO] | +- org.apache.commons:commons-text:jar:1.3:compile
[INFO] | +- commons-beanutils:commons-beanutils:jar:1.9.3:compile
[INFO] | | +- commons-logging:commons-logging:jar:1.2:compile
[INFO] | | \- commons-collections:commons-collections:jar:3.2.2:compile
[INFO] | \- org.apache.commons:commons-collections4:jar:4.2:compile
[INFO] +- jlibdiff:jlibdiff:jar:1.01:compile
[INFO] +- org.slf4j:slf4j-api:jar:1.7.7:compile
[INFO] +- org.slf4j:jcl-over-slf4j:jar:1.7.7:runtime
[INFO] +- org.slf4j:slf4j-log4j12:jar:1.7.7:runtime
[INFO] +- log4j:log4j:jar:1.2.17:compile
[INFO] \- junit:junit:jar:4.11:test
[INFO] \- org.hamcrest:hamcrest-core:jar:1.3:test
mylib pom.xml
<dependencies>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-api</artifactId>
<version>2.11.2</version>
</dependency>
<dependency>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-core</artifactId>
<version>2.11.2</version>
</dependency>
</dependencies>
CLASSPATH=$APP_HOME/lib/myproject-1.30.0.jar:$APP_HOME/lib/ojdbc6.jar:$APP_HOME/lib/jlibdiff-1.01.jar:$APP_HOME/lib/commons-cli-1.2.jar:$APP_HOME/lib/commons-io-2.4.jar:$APP_HOME/lib/commons-exec-1.3.jar:$APP_HOME/lib/commons-lang-2.6.jar:$APP_HOME/lib/slf4j-api-1.7.7.jar:$APP_HOME/lib/jcl-over-slf4j-1.7.7.jar:$APP_HOME/lib/slf4j-log4j12-1.7.7.jar:$APP_HOME/lib/log4j-1.2.17.jar:$APP_HOME/lib/mylib-1.0.0.jar
The $APP_HOME/lib contains all slf4j and log4j libraries and mylib as well.

Answer 1

My quick quess is, that you have two different versions of log4j on classpath. In dependency tree I see org.apache.logging.log4j:log4j-api:jar:2.11.2, but also log4j:log4j:jar:1.2.17. You have excluded transitional dependency org.apache.logging.log4j:log4j-core from mylib, but log4j-api is still there.
Try to remove the exclusion of org.apache.logging.log4j:log4j-core and also remove log4j:log4j:jar:1.2.17 from project. This way there should be just one version of log4j 2.11.2.