hey channel … I’m Java developer and newcomer with...

# getting-started

[Alexandre A Barbosa]

hey channel …
I’m Java developer and newcomer with Kotlin.
I’ve been working on a Kotlin/Springboot and Kafka application. I am using the KafkaListener and it requires a const val for name of the topic. This information comes from a parameter. Even if I assign the value to a new variable I get this issue…
Could you please help me to implement that correctly?

[Luis Mirabal]

I don't think you can do that in kotlin or java. But it looks like you could use expression language: https://stackoverflow.com/questions/54038928/how-to-pass-dynamic-topic-name-to-kafkalistenertopics-from-environment-variab

[Benoît Liessens]

Try passing the @Value through the constructor instead

[Alexandre A Barbosa]

humm… let me try that

[Alexandre A Barbosa]

nope

[Luis Mirabal]

The value needs to be known at compilation time, that's why it won't allow you to use variables and suggests a constant

[Benoît Liessens]

And with a val in the constructor?

[Alexandre A Barbosa]

yeah

[Alexandre A Barbosa]

let me try again

[Alexandre A Barbosa]

I guess you @Luis Mirabal is right. It can not be done like I tried with @Value

[Alexandre A Barbosa]

let me try with Autowired

[Alexandre A Barbosa]

not working…

[Jacob]

pretty sure you can use a SPEL for the topic name

[Alexandre A Barbosa]

hey @Jacob
you mean… something like this?
@KafkaListener(topics = [(“\#{T(package.name.TopicNameValue.Class).CONST}“)], groupId = “ingestion-consumer-groupid”)

[Jacob]

https://docs.spring.io/spring-kafka/docs/current/api/org/springframework/kafka/annotation/KafkaListener.html#topics()

[Jacob]

@KafkaListener(topics =["\${myTopicProperty}"]

[Jacob]

My SPel skills are weak But I do recall using the spel capabilities on the annotation to be able to dynamically set the topicname from the spring "environment"

[Alexandre A Barbosa]

I see… thank you Jacob.
I will update here once I manage finish this…

[Alexandre A Barbosa]

I get this…

[Alexandre A Barbosa]

my Class

class TopicNameValue {
    companion object {
        @Value("\${ingestion.config.topic.name}")
        lateinit var topicIngestionName: String
    }
}

[Alexandre A Barbosa]

and this Service

@KafkaListener(topics =["\${topicIngestionName}"], groupId = "ingestion-consumer-groupid")
fun consumeIngestion(message: String) {
    println("consumed message: $message")
}

[Alexandre A Barbosa]

Working fine, just like this:

@KafkaListener(
    topics = ["#{'\${ingestion.config.topic.name}'.split(',')}"],
    groupId = "ingestion-consumer-groupid")
fun consumeIngestion(message: String) {
    println("consumed message: $message")
}

[Alexandre A Barbosa]

Credits to this post

https://stackoverflow.com/questions/57953246/pass-array-list-of-topic-names-to-kafkalistener/57958423#57958423