add custom prometheus metric

add tests for kafka consumer

src/main/kotlin/com/example/demo/config/KafkaConsumerConfig.kt

@@ -2,6 +2,7 @@ package com.example.demo.config
 
 import com.example.demo.services.database.city.CityService
 import com.example.demo.services.kafka.Consumer
+import io.micrometer.core.instrument.MeterRegistry
 import org.apache.kafka.clients.consumer.ConsumerConfig
 import org.apache.kafka.common.serialization.StringDeserializer
 import org.springframework.beans.factory.annotation.Autowired
@@ -18,15 +19,20 @@ class KafkaConsumerConfig(
     @Bean
     fun consumer(
         @Autowired cityService: CityService,
-    ): Consumer = Consumer(cityService)
+        @Autowired metricRegistry: MeterRegistry
+    ): Consumer = Consumer(
+        cityService = cityService,
+        metricRegistry = metricRegistry,
+    )
 
     @Bean
     fun consumerFactory(): ConsumerFactory<String, String> {
         val configs = mapOf(
             ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG to kafkaProperties.bootstrapServers,
             ConsumerConfig.GROUP_ID_CONFIG to kafkaProperties.consumer.groupId,
+            ConsumerConfig.AUTO_OFFSET_RESET_CONFIG to kafkaProperties.consumer.autoOffsetReset,
             ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG to StringDeserializer::class.java,
-            ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG to StringDeserializer::class.java,
+            ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG to StringDeserializer::class.java
         )
 
         return DefaultKafkaConsumerFactory(configs)

src/main/kotlin/com/example/demo/config/KafkaProperties.kt

@@ -22,6 +22,7 @@ data class KafkaProperties @ConstructorBinding constructor(
         val groupId: String,
         val topics: String,
         val autoStartup: Boolean,
+        val autoOffsetReset: String,
     )
 
     data class Validation(

src/main/kotlin/com/example/demo/services/kafka/Consumer.kt

@@ -2,6 +2,8 @@ package com.example.demo.services.kafka
 
 import com.example.demo.services.database.city.CityService
 import com.example.demo.services.kafka.dto.CityCreateDto
+import io.micrometer.core.instrument.Counter
+import io.micrometer.core.instrument.MeterRegistry
 import kotlinx.serialization.json.Json
 import org.springframework.kafka.annotation.KafkaListener
 import org.springframework.messaging.handler.annotation.Payload
@@ -10,6 +12,7 @@ import org.springframework.stereotype.Component
 @Component
 class Consumer(
     private val cityService: CityService,
+    private val metricRegistry: MeterRegistry,
 ) {
     @KafkaListener(
         topics = ["#{'\${kafka.consumer.topics}'.split(',')}"],
@@ -17,6 +20,13 @@ class Consumer(
     )
     fun handleCityCreate(@Payload message: String) {
         val cityCreateDto = Json.decodeFromString<CityCreateDto>(message)
+            .also {
+                val counter = Counter.builder("kafka_consumer_city_create")
+                    .description("consumed created city event")
+                    .register(metricRegistry)
+                counter.increment()
+            }
+
         cityService.create(cityCreateDto)
     }
 }