from py4j.java_gateway import JavaGateway, GatewayParameters

  gateway=JavaGateway(gateway_parameters=GatewayParameters
  (port=port.port))

  promo_engine = gateway.entry_point

  order_json_string = promo_engine.placeOrder(1L, True, 1L, "true",
  None, "1PAY", False, cart)

GatewayServer gatewayServer1 = new GatewayServer(new
   PromotionBO(),port);
   gatewayServer1.start();

public Order placeOrder() {
//some logic
// this is the function which is called from python
}