Kafka를 사용한 데이터 동기화 코드 및 문서 추가

catalog-service/build.gradle

@@ -1,6 +1,7 @@
 dependencies {
     implementation(project(":util"))
 
+    implementation 'org.springframework.kafka:spring-kafka'
     implementation 'org.springframework.boot:spring-boot-starter-web'
     implementation 'org.springframework.boot:spring-boot-starter-validation'
     implementation 'org.springframework.boot:spring-boot-starter-data-jpa'

catalog-service/src/main/java/com/roy/springcloud/catalogservice/config/KafkaConsumerConfig.java

@@ -0,0 +1,36 @@
+package com.roy.springcloud.catalogservice.config;
+
+import org.apache.kafka.clients.consumer.ConsumerConfig;
+import org.apache.kafka.common.serialization.StringDeserializer;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.kafka.annotation.EnableKafka;
+import org.springframework.kafka.config.ConcurrentKafkaListenerContainerFactory;
+import org.springframework.kafka.core.ConsumerFactory;
+import org.springframework.kafka.core.DefaultKafkaConsumerFactory;
+
+import java.util.HashMap;
+import java.util.Map;
+
+@EnableKafka
+@Configuration
+public class KafkaConsumerConfig {
+
+    @Bean
+    public ConsumerFactory<String, String> consumerFactory() {
+        Map<String, Object> properties = new HashMap<>();
+        properties.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "127.0.0.1:9092");
+        properties.put(ConsumerConfig.GROUP_ID_CONFIG, "consumerGroupId");
+        properties.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
+        properties.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
+        return new DefaultKafkaConsumerFactory<>(properties);
+    }
+
+    @Bean
+    public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory() {
+        ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory = new ConcurrentKafkaListenerContainerFactory<>();
+        kafkaListenerContainerFactory.setConsumerFactory(consumerFactory());
+        return kafkaListenerContainerFactory;
+    }
+
+}

catalog-service/src/main/java/com/roy/springcloud/catalogservice/service/KafkaConsumer.java

@@ -0,0 +1,5 @@
+package com.roy.springcloud.catalogservice.service;
+
+public interface KafkaConsumer {
+    void processMessage(String kafkaMessage);
+}

catalog-service/src/main/java/com/roy/springcloud/catalogservice/service/impl/KafkaConsumerImpl.java

@@ -0,0 +1,48 @@
+package com.roy.springcloud.catalogservice.service.impl;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.type.TypeReference;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.roy.springcloud.catalogservice.domain.Catalog;
+import com.roy.springcloud.catalogservice.repository.CatalogRepository;
+import com.roy.springcloud.catalogservice.service.KafkaConsumer;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.kafka.annotation.KafkaListener;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class KafkaConsumerImpl implements KafkaConsumer {
+    private final CatalogRepository catalogRepository;
+
+    @Override
+    @Transactional
+    @KafkaListener(topics = "example-order-topic")
+    public void processMessage(String kafkaMessage) {
+        log.info("Kafka Message: ======> {}", kafkaMessage);
+
+        Map<Object, Object> map = new HashMap<>();
+        ObjectMapper mapper = new ObjectMapper();
+        try {
+            map = mapper.readValue(kafkaMessage, new TypeReference<>() {});
+        } catch (JsonProcessingException e) {
+            e.printStackTrace();
+        }
+
+        String targetProduceId = (String) Optional.of(map.get("productId"))
+                .orElseThrow(() -> new IllegalStateException("Not found produceId"));
+        Catalog savedCatalog = catalogRepository.findByProductId(targetProduceId)
+                .orElseThrow(() -> new IllegalStateException("Not found catalog"));
+        Integer soldQuantity = (Integer) Optional.of(map.get("quantity"))
+                .orElseThrow(() -> new IllegalStateException("Not found quantity"));
+        savedCatalog.setStock(savedCatalog.getStock() - soldQuantity);
+    }
+
+}