NoClassDefFoundError LogManager

PROBLEM:
NoClassDefFoundError: Could not initialize class org.apache.log4j.LogManager

SOLUTION:
remove:  -Dlog4j.configuration=file:conf/log4j.xml


Docs:
slf4j: https://www.slf4j.org/legacy.html
jars:
commons-logging-1.2.jar
jcl-over-slf4j-1.7.7.jar or jul-to-slf4j-1.7.12.jar
log4j-1.2.18*.jar
slf4j-api-1.7.12.jar
slf4j-log4j12-1.7.12.jar

PROBLEM:
Compilation failure
error: cannot access Consumer

SOLUTION:
Upgrade Java 1.7 to Java 1.8

Maven: Unable to find valid certification path to requested target

PROBLEM:
[ERROR] Failed to execute goal on project ***:
Could not resolve dependencies for project ***:
Failed to collect dependencies at ***
Failed to read artifact descriptor for ***
Could not transfer artifact *** sun.security.validator.ValidatorException:
PKIX path building failed:
sun.security.provider.certpath.SunCertPathBuilderException:
unable to find valid certification path to requested target

SOLUTION:
Create folder c:\Users\YOUR_NAME\certs\
Put keys *.cer and certs in it
Run:
mvn -Djavax.net.ssl.trustStore="c:\Users\YOUR_NAME\certs\cacerts" -Dmaven.wagon.http.ssl.ignore.validity.dates=true  -Dmaven.wagon.http.ssl.insecure=true -Dmaven.wagon.http.ssl.allowall=true  clean install