title: How to add the username to the log filename?
body: <p>I am using Log4j to log some information and I am trying to concatenate the current username to the log filename. This is what I am doing.</p>
  
  <p>log4j.appender.file.File=${userId}_file.log</p>
  
  <p>The filename being generated is _file.log. How to add the username or userId to the log filename?</p>