feat: 컨슈머 기능 구현

- 3개의 워커스레드 생성 및 실행
- 스프링의 PreDestroy를 이용한 shutdown 로직 구현

src/main/java/com/sangdol/consumer/infrastructure/kafka/consumer/MultiWorkerConsumer.java

@@ -0,0 +1,76 @@
+package com.sangdol.consumer.infrastructure.kafka.consumer;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.TimeUnit;
+
+import org.apache.kafka.clients.consumer.KafkaConsumer;
+import org.springframework.boot.context.event.ApplicationReadyEvent;
+import org.springframework.context.event.EventListener;
+import org.springframework.stereotype.Component;
+
+import com.sangdol.consumer.domain.TestRecord;
+import com.sangdol.consumer.infrastructure.kafka.producer.DLTProducer;
+
+import jakarta.annotation.PreDestroy;
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+@Component
+public class MultiWorkerConsumer {
+
+	private final ConsumerConfiguration consumerConfiguration;
+	private final DLTProducer dltProducer;
+	private final ConsumerStats consumerStats;
+	private final ExecutorService executorService;
+	private final Integer workerThreads;
+	private final List<ConsumerWorker> workers;
+
+	public MultiWorkerConsumer(
+		ConsumerConfiguration consumerConfiguration,
+		DLTProducer dltProducer,
+		ConsumerStats consumerStats,
+		ConsumerPool consumerPool
+	) {
+		this.consumerConfiguration = consumerConfiguration;
+		this.dltProducer = dltProducer;
+		this.consumerStats = consumerStats;
+		this.executorService = consumerPool.executorService();
+		this.workerThreads = consumerPool.poolSize();
+		this.workers = new ArrayList<>();
+	}
+
+	@EventListener(ApplicationReadyEvent.class)
+	public void initialize() {
+		log.info("[MultiWorkerConsumer] initialize");
+
+		for (int i = 0; i < workerThreads; i++) {
+			KafkaConsumer<String, TestRecord> consumer = consumerConfiguration.kafkaConsumer();
+			RecordProcessor recordProcessor = new RecordProcessor(dltProducer, consumerStats);
+			ConsumerWorker consumerWorker = new ConsumerWorker(consumer, recordProcessor);
+			workers.add(consumerWorker);
+			executorService.execute(consumerWorker);
+		}
+	}
+
+	@PreDestroy
+	public void shutdown() {
+		log.info("[MultiWorkerConsumer] Shutting down consumers..");
+		workers.forEach(ConsumerWorker::shutdown);
+		executorService.shutdown();
+
+		try {
+			if (!executorService.awaitTermination(30, TimeUnit.SECONDS)) {
+				log.warn("[MultiWorkerConsumer] Executor service did not terminated during 30 seconds. shutdown now.");
+				executorService.shutdownNow();
+			}
+		} catch (InterruptedException e) {
+			log.warn("[MultiWorkerConsumer] Interrupted while waiting for executors to terminate. shutdown now.");
+			executorService.shutdownNow();
+			Thread.currentThread().interrupt();
+		}
+
+		log.info("[MultiWorkerConsumer] Shutdown complete.");
+	}
+}