public HBaseRpcController newController(ExtendedCellScanner cellScanner) {
    return new HBaseRpcControllerImpl(null, cellScanner);
  }
Custom RPC Controller factory allows frameworks to change the RPC controller. If the configured
controller cannot be found in the classpath or loaded, we fall back to the default RPC
controller factory.
hbase-client/src/main/java/org/apache/hadoop/hbase/ipc/RpcControllerFactory.java