Publish multiple events shares some attributes in one kafka topic - spring-boot

Question

I need to publish multiple messages from the same project which represents employee journey events, and i need to use one topic only to publish these messages as they are representing the same project, but in some cases the message may contain extra fields for example:
All messages share (id, name, type, date) and
may some events have more fields like (course id, course name), so I am intending to use one parent object called "Journey", contains "Event" object, and I will create multiple children objects like 'LMSEvent' that extends this Event, etc if needed. Also using the Jackson + spring boot over rest APIs to do the needed cast based on type attribute. Finally, then this message to Kafka directly, so, each object contains its own properties.
For the consumer, I will do some strategy patterns and do the required logic per each type if needed.
The message size will not be very big and i don't expect to have more different attributes per each event.
I am looking to know if this approach is good or not and in case is not, what is the alternative.

Answer 1

I think that in general it is good approach. Having single message schema on topic or multiple schemas is always good question and both has some bright sights and drawbacks, you can read more about it in Martin Kleppmann article.
When you decided to have multiple events on single topic, starting from rest api and next by Kafka producer and consumer you can use the same approach of serializing and deserializing events, #JsonTypeInfo and #JsonSubTypes does the job:
#JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.EXISTING_PROPERTY,
property = "type")
#JsonSubTypes({
#JsonSubTypes.Type(value = LMSEvent.class, name = "LMSEvent"),
#JsonSubTypes.Type(value = YetAnotherEvent.class, name = "YetAnotherEvent")
})
public interface Event {
String getType();
default boolean hasType(String type) {
return getType().equalsIgnoreCase(type);
}
default <T> T getConcreteEvent(Class<T> clazz) {
return clazz.cast(this);
}
}
When you consume that type of messages using spring-kafka you can define some very neat code, where each method is consuming concrete event type, so you don't need to write some dirty casting by your own:
#KafkaListener(topics = "someEvents", containerFactory = "myKafkaContainerFactory")
public class MyKafkaHandler {
#KafkaHandler
void handleLMSEvent(LMSEvent event) {
....
}
#KafkaHandler
void handleYetAnotherEvent(YetAnotherEvent yetAnotherEvent) {
...
}
#KafkaHandler(isDefault = true)
void handleDefault(#Payload Object unknown,
#Header(KafkaHeaders.OFFSET) long offset,
#Header(KafkaHeaders.RECEIVED_PARTITION) int partitionId,
#Header(KafkaHeaders.RECEIVED_TOPIC) String topic) {
logger.info("Server received unknown message {},{},{}", offset, partitionId, topic);
}
}
Full code