title: Converting log4j.properties to log4j.xml
body: <p>I couldn't find anywhere how to specify constants in log4j.xml. For example, I have this constant in my log4j.properties:</p>
  
  <pre><code>#Log directory
  dal.log.dir=/var/log/pojodal/
  # Log filename
  dal.log.file=pojodal.log
  </code></pre>
  
  <p>And I use these constants as follows, in other parts of the properties file:</p>
  
  <pre><code>log4j.appender.DRFA1.File=${dal.log.dir}/${dal.log.file}
  </code></pre>
  
  <p>How to achieve the same behavior in log4j.xml?</p>