How to publish a message to Kafka topic using spring cloud stream in reactive way [using webflux]?

Question

• Publish a message to kafka topic without using StreamBridge as it uses deprecated components.

Answer 1

Using reactor API:

All you need to do is declare a Supplier<Flux<whatever>> which returns EmitterProcessor from the reactor API (see Reactive Functions support for more details) to effectively provide a bridge between the actual event source (foreign source) and spring-cloud-stream. All you need to do now is feed the EmitterProcessor with data via EmitterProcessor#onNext(data) operation.
Quoted from spring cloud stream docs

@SpringBootApplication
@Controller
public class WebSourceApplication {

    public static void main(String[] args) {
        SpringApplication.run(WebSourceApplication.class);
    }

    EmitterProcessor<String> processor = EmitterProcessor.create();

    @RequestMapping
    @ResponseStatus(HttpStatus.ACCEPTED)
    public void delegateToSupplier(@RequestBody String body) {
        processor.onNext(body);
    }

    @Bean
    public Supplier<Flux<String>> supplier() {
        return () -> this.processor;
    }
}

To send a message use curl curl -H "Content-Type: text/plain" -X POST -d "hello from the other side" http://localhost:8080/