Kafka - spring cloud stream - apache-kafka

Question

I am trying to use spring-cloud-stream with kafka. Below is the sample code. But it does not seem to do anything. It always creates a topic called 'output'. But the values are not published.
application.yaml
spring.cloud.stream:
function:
definition: streamSupplier
bindings:
streamSupplier-out-0:
destination: numbers
My aim is to just produce values.
#SpringBootApplication
#EnableBinding(Source.class)
public class CloudStreamDemoApplication {
private AtomicInteger atomicInteger = new AtomicInteger();
public static void main(String[] args) {
SpringApplication.run(CloudStreamDemoApplication.class, args);
}
#Bean
public Supplier<Integer> streamSupplier(){
return () -> {
System.out.println("Publishing : " + atomicInteger.incrementAndGet());
return atomicInteger.get();
};
}
}
dependency - 2.2.6.RELEASE
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-stream</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-stream-binder-kafka</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.kafka</groupId>
<artifactId>spring-kafka</artifactId>
</dependency>

Answer 1

You need to remove #EnableBinding(Source.class) from the class. If that is present, the functional bindings will not take place.

Answer 2

Annotation #EnableBinding has caused the issue as explained above.
Read the below excerpts from spring Docs:
Unlike previous versions of spring-cloud-stream which relied on #EnableBinding and #StreamListener annotations, the above example looks no different then any vanilla spring-boot application. It defines a single bean of type Function and that it is. So, how does it became spring-cloud-stream application? It becomes spring-cloud-stream application simply based on the presence of spring-cloud-stream and binder dependencies and auto-configuration classes on the classpath effectively setting the context for your boot application as spring-cloud-stream application. And in this context beans of type Supplier, Function or Consumer are treated as defacto message handlers triggering binding of to destinations exposed by the provided binder following certain naming conventions and rules to avoid extra configuration.