KafkaListener and __listener @KafKaListener can't resolve 'null' with Aspect Annotation

Question

I'm using @KafkaListener and I need a dynamic topic name so I use the SpEL '__listener' in order to do that

@PostConstruct
public void init() {
    myProps= generateTopicDynamically();
}

@KafkaListener(topics = "#{__listener.myProps}")
public void listenerKafka(@Payload MyObject myObject) {
       //Do something with my event
}

It works perfectly well.

The main issue is when I want to add another annotation that trigger some Aspect programmation

@MyCustomAnnotationToRecordPerformance @KafkaListener(topics = "#{__listener.myProps}") public void listenerKafka(@Payload MyObject myObject)

and here the aspect class

@Aspect
@Configuration
@Slf4j
public class MyCustomAnnotationToRecordPerformanceAspect {

    @Pointcut("@annotation(MyCustomAnnotationToRecordPerformance)")
    public void annotationMyCustomAnnotationToRecordPerformance() {
    }

    @Around("annotationMyCustomAnnotationToRecordPerformance()")
    public Object doSomething(final ProceedingJoinPoint proceedingJoinPoint) throws Throwable {
        return proceedingJoinPoint.proceed();
    }
}

I have this issue because Spring try to resolve __listener before @PostConstruct has been called.

Caused by: java.lang.IllegalArgumentException: @KafKaListener can't resolve 'null' as a String
    at org.springframework.kafka.annotation.KafkaListenerAnnotationBeanPostProcessor.resolveAsString(KafkaListenerAnnotationBeanPostProcessor.java:648)
    at org.springframework.kafka.annotation.KafkaListenerAnnotationBeanPostProcessor.resolveTopics(KafkaListenerAnnotationBeanPostProcessor.java:520)
    at org.springframework.kafka.annotation.KafkaListenerAnnotationBeanPostProcessor.processListener(KafkaListenerAnnotationBeanPostProcessor.java:419)
    at org.springframework.kafka.annotation.KafkaListenerAnnotationBeanPostProcessor.processKafkaListener(KafkaListenerAnnotationBeanPostProcessor.java:370)
    at org.springframework.kafka.annotation.KafkaListenerAnnotationBeanPostProcessor.postProcessAfterInitialization(KafkaListenerAnnotationBeanPostProcessor.java:298)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:431)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:595)
    ... 41 common frames omitted

I tried to debug it We can see lot of CGLIB reference, so bean has been already proxified, but all properties are null. So I supposed Autowired and PostConstruct method has not been called yet

For now, I tried to delay the processor that manage @KafkaListener, but I was not able to find where I can change that without have to redefine fully Kafka configuration

@EnableKafka import KafkaListenerConfigurationSelector that is DeferredImportSelector.

Here the comment on this class

A {@link DeferredImportSelector} implementation with the lowest order to import a {@link KafkaBootstrapConfiguration} as late as possible.

So I supposed it already delay as late as possible based on the comment

I test it with @Transactional, and I have the same issue.

@Transactional 
@KafkaListener(topics = "#{__listener.myProps}")
public void listenerKafka(@Payload MyObject myObject)

Do have any idea about it?

The only alternative I see for now is split my class in 2 and create 2 beans. KafkaListener method call the other bean. But I found very strange to have to do that.

Thanks in advance for you help.

An [MCVE](https://stackoverflow.com/help/mcve) on GitHub would help. Reproducing the problem is the first step in solving it. Besides, an `@Aspect` should be a `@Component`, not a `@Configuration`. I have no idea why so many people get that wrong. I cannot promise that it will help you to solve the problem, but it might. Either way, you ought to change it. Configuration vs. component proxies behave in different ways. — kriegaex, Nov 03 '21 at 05:35
Yes, agree @kriegaex, it was a component initialy, I tried different think, and forgot to came back to Component. Thanks for notice. — Thibaut, Nov 04 '21 at 13:40

Gary Russell · Answer 1 · 2021-11-03T14:30:42.243

I just tested it with @Transactional and it works as expected for me - I have confirmed that we already have a CGLIB proxy by the time we get to the @KafkaListener annotation BPP...

@SpringBootApplication
@EnableTransactionManagement
public class So69817946Application {

    public static void main(String[] args) {
        SpringApplication.run(So69817946Application.class, args);
    }

    @Bean
    public NewTopic topic() {
        return TopicBuilder.name("so69817946").partitions(1).replicas(1).build();
    }

}

@Component
class listener {

    public String getTopic() {
        return "so69817946";
    }

    @Transactional
    @KafkaListener(id = "so69817946", topics = "#{__listener.topic}")
    public void listen(String in) {
        System.out.println(in);
    }

}

@Component
class TM extends AbstractPlatformTransactionManager {

    @Override
    protected Object doGetTransaction() throws TransactionException {
        return new Object();
    }

    @Override
    protected void doBegin(Object transaction, TransactionDefinition definition) throws TransactionException {
    }

    @Override
    protected void doCommit(DefaultTransactionStatus status) throws TransactionException {
    }

    @Override
    protected void doRollback(DefaultTransactionStatus status) throws TransactionException {
    }

}

so69817946: partitions assigned: [so69817946-0]

And I can see the transaction interceptor in the call stack.

So, yes, an MCVE would be helpful.

So many time lost for that, I should think about it before. In case of Aspect, the bean processor use proxified getter and do not have access to private properties. I think about when I saw your getTopic method So I create a getter getMyProps() and it works If you change your code private topic="so69817946" without any getter, you would reproduce the issue. Thank you to gave me the missing clue. — Thibaut, Nov 04 '21 at 13:38
Yes; you must add a getter. Did you mean a `public` field? SpEL can't access `private` fields. `EL1008E: Property or field 'topic' cannot be found ` - if I change it to public, I get the `null` problem. — Gary Russell, Nov 04 '21 at 13:52
The property was public at the beginning to make SpEL working, but with Aspect and CGLib, only the getter works. I made and answer with the solution. Really thanks. — Thibaut, Nov 04 '21 at 14:02

score 0 · Answer 2 · answered Nov 04 '21 at 13:59

Thanks to the help of Gary, I found the solution. Once we have aspect, the class is proxified and properties became null in the CGLIB object. We need to call getter in order to have the value from original object, not the proxified one

SpEL is able to read public getter that will be executed on the original object, and not the CGLIB one

So the solution was simply to create a public getter for my private

public String getMyProps(){
    return this.myProps;
}

Thanks all.

This saved my day. I have spent quite a few hours. Thanks. – YamYamm Jul 27 '23 at 07:34 — YamYamm, Jul 27 '23 at 07:34

KafkaListener and __listener @KafKaListener can't resolve 'null' with Aspect Annotation

2 Answers2