title: How to Dynamically change a logback variable (filename)?
body: <p>I am currently working on a spring-boot batch application who detect new files and read them. All is working well, but i have a problem with the filename of the logs.
  The thing is, the filename of each log (one for each file) must be created dynamically while the batch is running, and i don't know how to change dynamically the log's filename in the logback. </p>
  
  <p>This is my logback for the moment (${TECH} is what i want to change) :</p>
  
  <pre><code>&lt;configuration debug="false" scan="true" scanPeriod="30 seconds"&gt;
      &lt;springProperty scope="context" name="directory.log.tech" source="bpa.batch.directory.log.technique"/&gt;
      &lt;appender name="TECHNIQUE" class="ch.qos.logback.core.rolling.RollingFileAppender"&gt;
          &lt;filter class="ch.qos.logback.classic.filter.LevelFilter"&gt;
              &lt;level&gt;DEBUG&lt;/level&gt;
              &lt;onMatch&gt;DENY&lt;/onMatch&gt;
              &lt;onMismatch&gt;ACCEPT&lt;/onMismatch&gt;
          &lt;/filter&gt;
          &lt;rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy"&gt;
              &lt;fileNamePattern&gt;${directory.log.tech}\%d{yyyyMMdd}.${TECH}.log&lt;/fileNamePattern&gt;
          &lt;/rollingPolicy&gt;
          &lt;encoder&gt;
              &lt;pattern&gt;%msg%n&lt;/pattern&gt;
          &lt;/encoder&gt;
      &lt;/appender&gt;
  
      &lt;logger name="fr.hm.bpa.log.LogTechnique" level="TRACE"&gt;
          &lt;appender-ref ref="TECHNIQUE" /&gt;
      &lt;/logger&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p>Could someone explain how to change it while my code is running ? Thanks in advance.</p>