title: Referencing java class variable from log4j2.xml configuration
body: <p>I am using log4j2 and using log4j2.xml for its configuration. I am configuring the <code>PatternLayout</code> and its pattern currently is <code>%d [%t] %p %c - %m%n</code>. It is the same value as <code>PatternLayout.SIMPLE_CONVERSION_PATTERN</code> defined in log4j2 core Javadoc. So is it possible to reference this variable instead of copy the value into the xml?</p>
  
  <p>My full log4j2.xml is attached for your reference.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;Configuration status="WARN"&gt;
      &lt;Appenders&gt;
          &lt;Console name="consoleAppender" target="SYSTEM_OUT"&gt;
              &lt;PatternLayout pattern="%d [%t] %p %c - %m%n" /&gt;
          &lt;/Console&gt;
      &lt;/Appenders&gt;
      &lt;Loggers&gt;
          &lt;Root level="ALL"&gt;
              &lt;AppenderRef ref="consoleAppender" /&gt;
          &lt;/Root&gt;
      &lt;/Loggers&gt;
  &lt;/Configuration&gt;
  </code></pre>