title: log4j. Unique log-file name
body: <p>How I can create a uniquely named log file using <code>log4j</code>?. When I used <code>Logback</code>, I can do it like this: </p>
  
  <pre><code> &lt;!-- current time formatted as "yyyyMMdd'T'HHmmss".  This value will be available to all 
      subsequent configuration elements. --&gt;
  &lt;timestamp key="bySecond" datePattern="yyyyMMdd'T'HHmmss" /&gt;
  </code></pre>
  
  <p>and inside logger appender define file name pattern:</p>
  
  <pre><code>&lt;file&gt;${bySecond}.log&lt;/file&gt;
  </code></pre>