title: Adding date to logback.xml
body: <p>Have tried to search for it but I keep on getting <code>...IS_UNDEFINED</code> as my file name. I simply want to append the current date to a log file. Any simple example for the logback.xml file?</p>
  
  <p>This is my latest try:</p>
  
  <pre><code>&lt;Properties&gt;
    &lt;property name="filePattern"&gt;log_${date:yyyy-MM-dd}.log&lt;/property&gt;
  &lt;/Properties&gt;
  &lt;appender name="FILE" class="ch.qos.logback.core.FileAppender"&gt;
    &lt;file&gt;${application.home:-.}/logs/${filePattern}&lt;/file&gt;
    &lt;encoder&gt;
      &lt;pattern&gt;%date [%level] from %logger in %thread - %message%n%xException&lt;/pattern&gt;
    &lt;/encoder&gt;
  &lt;/appender&gt;
  </code></pre>