title: common variable for log4j.xml configuration
body: <p>I have log4j.xml configuration like this:</p>
  
  <pre><code>&lt;appender name="MyAppender"class="org.apache.log4j.DailyRollingFileAppender"&gt;   
       &lt;param name="File"     value="/logs/custom/my.log"/&gt;
  ...  
   &lt;/appender&gt;
  </code></pre>
  
  <p>However the root directory of my file are the same for a lot of appender. Is there a way to defined "/logs/custom/" as a variable and reused it in all of my appender.</p>
  
  <p>Thanks,</p>
  
  <p>Sean</p>