title: Logback: Multiple Property Sources
body: <p>I want to do something like:</p>
  
  <pre><code>&lt;insertFromJNDI env-entry-name="java:comp/env/conf/app-log-path" as="logPath" /&gt;
  &lt;if test='!isDefined("logPath") &amp;amp;&amp;amp; isDefined("catalina.home")'&gt;
    &lt;then&gt;
      &lt;property name="logPath" value="${catalina.home}/logs/" /&gt;
    &lt;/then&gt;
  &lt;/if&gt;
  &lt;appender name="ROLLING_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender"&gt;
      &lt;file&gt;${logPath:-logs/}myapp.log&lt;/file&gt;
  &lt;/appender&gt;   
  </code></pre>
  
  <p>that is, allow a JNDI property to be sent in to my logging configuration, and if that is not found then try using catalina.home, and if that is not found then use a default value.  Is this possible?  It seems to me that is should be, but the  never seems to take effect, maybe properties can't be updated in this manner?  The documentation (chapter 3 of the manual) makes the property substituton seem quite powerful, but I just can't seem to get it working properly.</p>