This is an infix expression parser and Reverse Polish notation (RPN) evaluator.
Based off of Mathematical Expression Parsers in Java and C++ over at technical-recipes.com.
Configure the main class to use the log4j2.json file:
-Dlog4j.configurationFile=src/main/resources/rpn/calculator/core/log4j2.json
In Eclipse, under Run Configurations, the argument above should be pasted in the VM arguments section.
Submit a pull request, after forking and modifying.