import com.google.common.util.concurrent.AbstractCheckedFuture; //导入依赖的package包/类
private CheckedFuture<Void, RpcException> connect(final UserToBitHandshake handshake,
    final DrillbitEndpoint endpoint) {
  final SettableFuture<Void> connectionSettable = SettableFuture.create();
  final CheckedFuture<Void, RpcException> connectionFuture =
      new AbstractCheckedFuture<Void, RpcException>(connectionSettable) {
        @Override protected RpcException mapException(Exception e) {
          return RpcException.mapException(e);
        }
      };
  final RpcConnectionHandler<UserToBitConnection> connectionHandler =
      new RpcConnectionHandler<UserToBitConnection>() {
        @Override public void connectionSucceeded(UserToBitConnection connection) {
          connectionSettable.set(null);
        }

        @Override public void connectionFailed(FailureType type, Throwable t) {
          connectionSettable
              .setException(new RpcException(String.format("%s : %s", type.name(), t.getMessage()), t));
        }
      };

  connectAsClient(queryResultHandler.getWrappedConnectionHandler(connectionHandler), handshake,
      endpoint.getAddress(), endpoint.getUserPort());

  return connectionFuture;
}