public void addProviderListener(ConsumerConfig consumerConfig, ProviderInfoListener listener) {
        if (listener != null) {
            RegistryUtils.initOrAddList(providerListenerMap, consumerConfig, listener);
        }
    }
Add provider listener.

@param consumerConfig the consumer config
@param listener       the listener
registry/registry-zk/src/main/java/com/alipay/sofa/rpc/registry/zk/ZookeeperProviderObserver.java