@Override public final String toString() {
    return "ActiveMQCollector{"
      + "brokerURL=" + lazyInit.connectionFactory.getBrokerURL()
      + ", queue=" + lazyInit.queue
      + "}";
  }
Count of concurrent message listeners on the queue. Defaults to 1
zipkin-collector/activemq/src/main/java/zipkin2/collector/activemq/ActiveMQCollector.java