CircuitBreaker will not open R4J - spring

Question

I am using kotlin, with Spring Boot and resilience4j.
I am trying to set up a circuitbreaker to trigger when my other service is down, but now when i send request in Postman, it goes into the "getCatById" still and keeps returning me 500 internal server error, instead of going into the callback i have set.
#Service
class CatGateway {
val logger = LoggerFactory.getLogger(CatGateway::class.java)
#Value("\${catservice.baseurl}")
lateinit var baseUrl: String
val GET_ENDPOINT = "/cat"
val restClient = RestTemplate();
#CircuitBreaker(name = "catGateway", fallbackMethod = "dogFallback")
fun getCatById(id: Int): Cat?{
val result = restClient.getForObject("$baseUrl/$GET_ENDPOINT/$id", ByteArray::class.java)
return jacksonObjectMapper().readValue(result, Cat::class.java )
}
fun dogFallback(t: Throwable): Cat?{
logger.error("Circuitbreaker opened")
throw CatNotFoundException("Cat not found, cause service broke");
}
}
data class Cat(val id: Int)
application.yml
catservice:
baseurl: "http://localhost:8080/api"
server:
port: 8085
resilience4j:
circuitbreaker:
configs:
shared:
register-health-indicator: true
sliding-window-type: count_based
sliding-window-size: 5
failure-rate-threshold: 40
permitted-number-of-calls-in-half-open-state: 1
max-wait-duration-in-half-open-state: 10s
wait-duration-in-open-state: 10s
slow-call-duration-threshold: 2s
writable-stack-trace-enabled: true
automatic-transition-from-open-to-half-open-enabled: true
instances:
catGateway:
base-config: shared
management:
health:
circuitbreakers:
enabled: true
endpoint:
health:
show-details: always
Dependencies:
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-circuitbreaker-resilience4j</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
<version>2.7.5</version>
</dependency>

Answer 1

I study the same thing today and this is my demo project.
You may just run user-service application to see the effect of circuit breaker
After searching through the internet, the annotation fallback method in resilience4j fail to work as the one in Java due to the exception handling mechanism of Kotlin(please correct me if I am wrong)
So we have to implement another mechanism to catch the exception and trigger the circuit breaker(you may see the circuit breaker status from the api return message caught by the exception handler).
If there is a better solution. Please let me know. Thanks
https://github.com/billchau/circuit-breaker-kotlin/tree/master