my customized Smart Service Plugin shows log4j class not defined error

Basiclly I follows the steps as mentioned in the document: https://docs.appian.com/suite/help/21.4/Appian_Plug-ins.html, However I runs into issues after deploy my plugin to Appian server.

1. I copied the log4j-core-2.17.1.jar and log4j-api-2.17.1.jar from /deployment/web.war/WEB-INF/lib folder to my laptop, and inlcude them to my project 

2. In my code, i use LogManager.getLogger(MyClass.class) to get a Logger (org.apache.logging.log4j.Logger)

3. Use Logger object to log messages

But when the code runs on Appian server, in log file shows exceptions about the org.apache.logging.log4j.Logger class is not defined. 

I am using Appian V21.4.