<configuration>

  <appender name="LIST" class="ch.qos.logback.core.read.ListAppender">

    <filter class="ch.qos.logback.classic.filter.LevelFilter">
      <OnMatch>DENY</OnMatch>
      <level>ERROR</level>
    </filter>
  </appender>

  <root level="debug">
    <appender-ref ref="LIST" />
  </root>
</configuration>