Quick one – I had this issue today so wanted to record it for posterity.
Tomcat can get confused if WEB-INF/lib contains the log4j jar, with initialisation errors such as:
java.lang.ClassNotFoundException: org.apache.log4j.Category
You might not even have directly included it – it might be included via a Maven dependency.
The solution is simple; remove log4j! It’s (often) already included in Tomcat, which is the root cause of the issues. If it’s a Maven dependency, add an exclusion.