apollo-core/src/main/java/com/ctrip/framework/apollo/tracer/internals/DefaultMessageProducerManager.java/DefaultMessageProducerManager/DefaultMessageProducerManager
class DefaultMessageProducerManager:  public DefaultMessageProducerManager() {
    if (ClassLoaderUtil.isClassPresent(CatNames.CAT_CLASS)) {
      producer = new CatMessageProducer();
    } else {
      producer = new NullMessageProducerManager().getProducer();
    }
  }