I'm facing a ClassCastException with Spring Cloud Bus when consuming EnvironmentBusRemoteApplicationEvent (triggered via /busenv endpoint) from a Kafka topic. The issue only occurs when I configure a named group.id on the consumer. With the default anonymous consumer group, everything works perfectly.

Environment

• Spring Boot: 3.3.10

• Spring Cloud Bus: 4.1.2

• Apache Kafka (with SSL)

Configuration

Here's the relevant part of my application.yaml:

yaml

spring:
  cloud:
    bus:
      enabled: true
      destination: XPTO.bus.2t
      id: xpto-api-stable:2t
      refresh.enabled: true
      env.enabled: true
      trace.enabled: true
    stream:
      bindings:
        springCloudBusInput:
          destination: XPTO.bus.2t
          group: ${HOSTNAME}  # Named group = POD_NAME (e.g., xpto-api-stable-7957c686d8-hfgz8)
          binder: kafka
        springCloudBusOutput:
          binder: kafka
      kafka:
        binder:
          brokers: ${KAFKA_BOOTSTRAP_SERVERS}
          configuration:
            client.id: ${spring.application.name}-${HOSTNAME}
            auto.offset.reset: latest
            security.protocol: SSL
            # ... SSL configuration omitted for brevity

The Problem

When group: ${HOSTNAME} is set (a named consumer group), consuming an EnvironmentBusRemoteApplicationEvent (triggered by POST /busenv) fails with:

text

java.lang.ClassCastException: class [B cannot be cast to class org.springframework.cloud.bus.event.RemoteApplicationEvent
  at org.springframework.cloud.bus.BusConsumer.accept(BusConsumer.java:31)

Full stack trace:

text

Caused by: java.lang.ClassCastException: class [B cannot be cast to class org.springframework.cloud.bus.event.RemoteApplicationEvent ([B is in module java.base of loader 'bootstrap'; org.springframework.cloud.bus.event.RemoteApplicationEvent is in unnamed module of loader org.springframework.boot.loader.launch.LaunchedClassLoader @5f282abb)
    at org.springframework.cloud.bus.BusConsumer.accept(BusConsumer.java:31)
    at org.springframework.cloud.function.context.catalog.SimpleFunctionRegistry$FunctionInvocationWrapper.invokeConsumer(SimpleFunctionRegistry.java:1063)
    ... 37 more

The message payload arrives as byte[224] instead of being deserialized into RemoteApplicationEvent.

What Works

1. Anonymous consumer group – If I remove the group property, the error disappears and /busenv works correctly:

yaml

spring:
  cloud:
    stream:
      bindings:
        springCloudBusInput:
          destination: XPTO.bus.2t
          # group: ${HOSTNAME}  # <-- commented out = anonymous group works fine

The kafka_groupId in logs changes to something like anonymous.e0f1240f-9b9b-494a-8b8a-63372c5123af, and deserialization works.

2. busrefresh endpoint – POST /busrefresh works correctly in both named and anonymous group scenarios. The issue is specific to busenv.

What I've Tried (with named group)

Adding explicit deserializer configuration for the consumer:

yaml

spring.cloud.stream.kafka.bindings.springCloudBusInput.consumer.configuration:
  key.deserializer: org.apache.kafka.common.serialization.StringDeserializer
  value.deserializer: org.springframework.kafka.support.serializer.JsonDeserializer

Setting spring.json.trusted.packages and spring.json.value.default.type:

yaml

spring.cloud.stream.kafka.bindings.springCloudBusInput.consumer.properties:
  spring.json.trusted.packages: "*"
  spring.json.value.default.type: org.springframework.cloud.bus.event.RemoteApplicationEvent

None of these resolved the issue. The ClassCastException persists only when using a named group.id with /busenv.

Questions

1. Why does EnvironmentBusRemoteApplicationEvent deserialization fail with a named consumer group, while RefreshRemoteApplicationEvent works fine?

2. Why does the anonymous group work perfectly for both event types?

3. What is the correct configuration to make busenv work with a named/persistent group.id in Kafka?

Additional Context

• I need a named group.id because my Kafka cluster's ACL policy does not allow anonymous groups (they are blocked by GroupAuthorizationException). The anonymous group approach is not viable in production.

Any help would be greatly appreciated!