private static String getRpcClientClass(Configuration conf) {
    String rpcClientClass = conf.get(CUSTOM_RPC_CLIENT_IMPL_CONF_KEY);
    if (rpcClientClass == null) {
      return NettyRpcClient.class.getName();
    }
    String mappedName = DEPRECATED_NAME_MAPPING.get(rpcClientClass);
    return mappedName == null ? rpcClientClass : mappedName;
  }
Creates a new RpcClient by the class defined in the configuration or falls back to
RpcClientImpl
@param conf      configuration
@param clusterId the cluster id
@param metrics   the connection metrics
@return newly created RpcClient
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcClientFactory.java