User Story

As an application developer, I want to see some log when a formula is evaluated or is ignored in any case. Hence, when something happens unexpectedly in the production server, I can check the log to debug. Because it's not easy to set a breakpoint or can't stop the service in the production environment to check the value in variables.

Details

• some classes use apache poi log, most classes use slf4j log. It's better to use the same log so that it's easy to enable them in the same way.
• according to log4j doc:

  void debug(String format, Object arg)
  Log a message at the DEBUG level according to the specified format and argument. This form avoids superfluous object creation when the logger is disabled for the DEBUG level.

  So just call that method without checking if(logger.isDebugEnabled())