OrderController.java

@Slf4j
@EnableBinding(OrderSource.class)
@RestController
public class OrderController
{
    @Autowired
    private OrderSource source;

    @PostMapping("/orders/publish")
    public String publishOrder(@RequestBody Order order, @RequestParam("payment_mode") String paymentMode)
    {
        source.create().send(MessageBuilder.withPayload(order).setHeader("payment_mode",paymentMode).build());
        log.info(order.toString());
        return "order_published";
    }
}