Pause message consumption from main kafka stream and start from other kafka topic

Question

I am using @StreamListener (spring cloud stream) to consume messages from a topic (input-channel), do some processing and save into some cache or database.

My requirement is, if DB goes down while processing the consumed message, I want to pause the main consumer(input-channel), and start consuming from another TOPIC (INPUT56-CHANNEL), and as soon as It consume all the message (doesn't have many) from INPUT56-CHANNEL, I want to resume the main consumer (input-channel) again.

Can that be achieved??

Answer 1

@StreamListener is deprecated; you should convert to the functional programming model instead.

Here is an example using that model (but the same techniques apply to the deprecated listeners).

spring.cloud.function.definition=input1;input2

spring.cloud.stream.bindings.input1-in-0.group=grp1
spring.cloud.stream.bindings.input2-in-0.consumer.auto-startup=false
spring.cloud.stream.bindings.input2-in-0.group=grp2

spring.cloud.stream.kafka.bindings.input2-in-0.consumer.idle-event-interval=5000

@SpringBootApplication
public class So69726610Application {

    public static void main(String[] args) {
        SpringApplication.run(So69726610Application.class, args);
    }

    boolean dbIsDown = true;

    @Autowired
    BindingsLifecycleController controller;

    TaskExecutor exec = new SimpleAsyncTaskExecutor();

    @Bean
    public Consumer<String> input1() {
        return str -> {
            System.out.println(str);
            if (this.dbIsDown) {
                this.controller.changeState("input1-in-0", State.PAUSED);
                this.controller.changeState("input2-in-0", State.STARTED);
                throw new RuntimeException("Paused");
            }
        };
    }

    @Bean
    public Consumer<String> input2() {
        return System.out::println;
    }

    @EventListener
    public void idle(ListenerContainerIdleEvent event) {
        System.out.println(event);
        // assumes concurrency = 1 (default)
        if (event.getListenerId().contains("input2-in-0")) {
            this.controller.changeState("input1-in-0", State.RESUMED);
            this.exec.execute(() -> this.controller.changeState("input2-in-0", State.STOPPED));
        }
    }

}