feat: Dead Letter Topic 프로듀서 기능 구현

- 최대 5회 재시도. 재시도 실패시 인메모리 컬렉션에 저장

src/main/java/com/sangdol/consumer/infrastructure/kafka/producer/DLTProducer.java

@@ -0,0 +1,70 @@
+package com.sangdol.consumer.infrastructure.kafka.producer;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.kafka.clients.producer.KafkaProducer;
+import org.apache.kafka.clients.producer.ProducerRecord;
+import org.springframework.retry.annotation.Backoff;
+import org.springframework.retry.annotation.Recover;
+import org.springframework.retry.annotation.Retryable;
+import org.springframework.stereotype.Component;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.sangdol.consumer.infrastructure.kafka.common.KafkaProperties;
+import com.sangdol.consumer.infrastructure.kafka.common.serialize.JsonObjectMapper;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+@Component
+@RequiredArgsConstructor
+public class DLTProducer {
+
+	private final KafkaProducer<String, String> dltProducer;
+	private final KafkaProperties.DeadLetterTopic deadLetterTopic;
+	private final JsonObjectMapper jsonObjectMapper;
+
+	// 실제 환경에서는 DB, 파일 시스템 등 외부에 저장 필요
+	private final List<FailedDltMessage> failed = new ArrayList<>();
+
+	@Retryable(
+		retryFor = {Exception.class},
+		maxAttempts = 5,
+		backoff = @Backoff(delay = 500, multiplier = 2),
+		listeners = {"dltRetryListener"}
+	)
+	public void sendToDeadLetterTopic(String key, Object value, Exception exception) throws Exception {
+		String valueJson = jsonObjectMapper.serialize(value);
+		String message = jsonObjectMapper.serialize(new DltMessage(exception.getMessage(), valueJson));
+		ProducerRecord<String, String> producerRecord = new ProducerRecord<>(deadLetterTopic.name(), key, message);
+
+		dltProducer.send(producerRecord).get();
+		log.info("[DLTProducer] Succeed to send. key : {}, value: {}", key, valueJson);
+	}
+
+	@Recover
+	public void recover(Exception last, String key, Object value, Exception origin) {
+		log.error("[DLTProducer] Failed to produce DLT message for key: {}, value: {} cause: {}", key, value, last.getMessage());
+		DltMessage dltMessage = new DltMessage(origin.getMessage(), jsonObjectMapper.serialize(value));
+		failed.add(new FailedDltMessage(key, dltMessage));
+	}
+
+	@VisibleForTesting
+	List<FailedDltMessage> getFailed() {
+		return failed;
+	}
+
+	record DltMessage(
+		String exception,
+		String message
+	) {
+	}
+
+	record FailedDltMessage(
+		String key,
+		DltMessage message
+	) {
+	}
+}

src/main/java/com/sangdol/consumer/infrastructure/kafka/producer/DLTRetryListener.java

@@ -0,0 +1,26 @@
+package com.sangdol.consumer.infrastructure.kafka.producer;
+
+import org.springframework.retry.RetryCallback;
+import org.springframework.retry.RetryContext;
+import org.springframework.retry.RetryListener;
+import org.springframework.stereotype.Component;
+
+import lombok.extern.slf4j.Slf4j;
+
+@Slf4j
+@Component("dltRetryListener")
+public class DLTRetryListener implements RetryListener {
+
+	@Override
+	public <T, E extends Throwable> void onError(
+		RetryContext context,
+		RetryCallback<T, E> callback,
+		Throwable throwable
+	) {
+		int retryCount = context.getRetryCount();
+		log.warn("[DLTProducer] Retry to send DLT message. Retry count: {}, Cause: {}", retryCount,
+			throwable.getMessage());
+
+		RetryListener.super.onError(context, callback, throwable);
+	}
+}