Threshold + Logger filter for Logback in Scala

ThresholdLoggerFilter.scala

package smartcontract.utils

import ch.qos.logback.classic.Level
import ch.qos.logback.classic.spi.ILoggingEvent
import ch.qos.logback.core.filter.Filter
import ch.qos.logback.core.spi.FilterReply


/**
 * Code rewritten from Java source
 * found on http://stackoverflow.com/questions/10734025/logback-two-appenders-multiple-loggers-different-levels
 */

class ThresholdLoggerFilter extends Filter[ILoggingEvent] {
  private var level: Level = _
  private var logger: String = _

  override def decide(event: ILoggingEvent): FilterReply = {
    if (!isStarted) {
      FilterReply.NEUTRAL
    } else if (!event.getLoggerName.startsWith(logger)) {
      FilterReply.DENY
    } else if (event.getLevel.isGreaterOrEqual(level)) {
      FilterReply.NEUTRAL
    } else {
      FilterReply.DENY
    }
  }


  def setLevel(level: Level) {
    this.level = level
  }

  def setLogger(logger: String) {
    this.logger = logger
  }

  override def start() {
    if (this.level != null && this.logger != null) {
      super.start()
    }
  }
}

If I understand this implementation correctly, then this filter only allows Loggers that begin with logger as all other loggers result in DENY. This would make using this filter for multiple loggers impossible:

<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
  <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
    <level>INFO</level>
  </filter>
  <filter class="smartcontract.utils.ThresholdLoggerFilter">
    <logger>org.springframework</logger>
    <level>ERROR</level>
  </filter>
  <filter class="smartcontract.utils.ThresholdLoggerFilter">
    <logger>org.example</logger>
    <level>INFO</level>
  </filter>
</appender>

Here both filters mutually exclude each other.