fix: 안읽음 카운트 Redis INCR 연산 직렬화 에러 해결

src/main/java/com/grabpt/service/ChatService/redis/UnreadCountChatService.java

@@ -3,6 +3,7 @@
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.data.redis.core.RedisTemplate;
+import org.springframework.data.redis.core.StringRedisTemplate;
 import org.springframework.stereotype.Service;
 
 import java.util.HashMap;
@@ -15,12 +16,12 @@
 @RequiredArgsConstructor
 public class UnreadCountChatService {
 
-	private final RedisTemplate<String, Object> redisTemplate;
+	//private final RedisTemplate<String, Object> redisTemplate;
+	private final StringRedisTemplate redisTemplate;
 
-	private String generateKey(Long roomId, Long userId){
-		return "chat:unread:"+roomId+":"+userId;
+	private String generateKey(Long roomId, Long userId) {
+		return "chat:room_unread:" + roomId + ":" + userId;
 	}
-
 	public void incrementUnreadCount(Long roomId, Long userId){
 		String key = generateKey(roomId, userId);
 		redisTemplate.opsForValue().increment(key);
@@ -42,7 +43,7 @@ public Map<Long, Long> getUnreadCounts(List<Long> roomIds, Long userId){
 			.toList();
 
 		// Redis MGET
-		List<Object> values = redisTemplate.opsForValue().multiGet(keys);
+		List<String> values = redisTemplate.opsForValue().multiGet(keys);
 
 		Map<Long, Long> resultMap = new HashMap<>();
 		for(int i=0; i<roomIds.size(); i++){

src/test/java/com/grabpt/service/ChatService/redis/UnreadCountChatServiceTest.java

@@ -0,0 +1,55 @@
+package com.grabpt.service.ChatService.redis;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.data.redis.core.StringRedisTemplate;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@Disabled("GitHub Actions 등 외부 CI 환경에서는 DB/Redis가 없어 실패하므로 제외")
+@SpringBootTest
+class UnreadCountCacheServiceTest {
+
+	@Autowired
+	private UnreadCountChatService unreadCountChatService;
+
+	@Autowired
+	private StringRedisTemplate redisTemplate; // 검증용
+
+	@Test
+	@DisplayName("최초 메시지 수신(INCR) 후 읽음 처리(SET 0)를 하고, 다시 수신(INCR)해도 에러가 나지 않아야 한다.")
+	void unreadCountLifeCycleTest() {
+		Long roomId = 1L;
+		Long userId = 1L;
+		String key = "chat:room_unread:" + roomId + ":" + userId;
+
+		redisTemplate.delete(key);
+
+		try {
+			// 1. 처음 메시지를 받음 (INCR) -> 성공해야 함
+			unreadCountChatService.incrementUnreadCount(roomId, userId);
+
+			// 2. 유저가 방에 들어와서 읽음 처리 (SET 0) -> 여기서 JSON으로 꼬이던 문제 발생 지점
+			unreadCountChatService.resetUnreadCount(roomId, userId);
+
+			// 3. 다시 메시지를 받음 (INCR) -> 에러가 터지지 않고 1이 되어야 함!
+			unreadCountChatService.incrementUnreadCount(roomId, userId);
+
+			// then (검증)
+			Map<Long, Long> result = unreadCountChatService.getUnreadCounts(List.of(roomId), userId);
+
+			// 최종 안읽음 개수는 1개여야 한다.
+			assertThat(result.get(roomId)).isEqualTo(1L);
+
+		} finally {
+			// 테스트 끝난 후 캐시 정리
+			redisTemplate.delete(key);
+		}
+	}
+}