.editorconfig

@@ -7,5 +7,5 @@ indent_size = 4
 indent_style = space
 trim_trailing_whitespace = true
 insert_final_newline = true
-max_line_length = 120
+max_line_length = 130
 tab_width = 4

src/main/kotlin/kr/co/vividnext/sodalive/chat/character/controller/ChatCharacterController.kt

@@ -64,7 +64,7 @@ class ChatCharacterController(
                 }
         }
 
-        // 인기 캐릭터 조회 (현재는 빈 리스트)
+        // 인기 캐릭터 조회
         val popularCharacters = service.getPopularCharacters()
             .map {
                 Character(

src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/ChatCharacterService.kt

@@ -16,6 +16,7 @@ import kr.co.vividnext.sodalive.chat.character.repository.ChatCharacterHobbyRepo
 import kr.co.vividnext.sodalive.chat.character.repository.ChatCharacterRepository
 import kr.co.vividnext.sodalive.chat.character.repository.ChatCharacterTagRepository
 import kr.co.vividnext.sodalive.chat.character.repository.ChatCharacterValueRepository
+import org.springframework.cache.annotation.Cacheable
 import org.springframework.data.domain.PageRequest
 import org.springframework.stereotype.Service
 import org.springframework.transaction.annotation.Transactional
@@ -26,16 +27,29 @@ class ChatCharacterService(
     private val tagRepository: ChatCharacterTagRepository,
     private val valueRepository: ChatCharacterValueRepository,
     private val hobbyRepository: ChatCharacterHobbyRepository,
-    private val goalRepository: ChatCharacterGoalRepository
+    private val goalRepository: ChatCharacterGoalRepository,
+    private val popularCharacterQuery: PopularCharacterQuery
 ) {
     /**
-     * 일주일간 대화가 가장 많은 인기 캐릭터 목록 조회
-     * 현재는 채팅방 구현 전이므로 빈 리스트 반환
+     * UTC 20:00 경계 기준 지난 윈도우의 메시지 수 상위 캐릭터 조회
+     * Spring Cache(@Cacheable) + 동적 키 + 고정 TTL(24h) 사용
      */
     @Transactional(readOnly = true)
-    fun getPopularCharacters(): List<ChatCharacter> {
-        // 채팅방 구현 전이므로 빈 리스트 반환
-        return emptyList()
+    @Cacheable(
+        cacheNames = ["popularCharacters_24h"],
+        key = "T(kr.co.vividnext.sodalive.chat.character.service.RankingWindowCalculator).now('popular-chat-character').cacheKey"
+    )
+    fun getPopularCharacters(limit: Long = 20): List<ChatCharacter> {
+        val window = RankingWindowCalculator.now("popular-chat-character")
+        val topIds = popularCharacterQuery.findPopularCharacterIds(window.windowStart, window.nextBoundary, limit)
+        return loadCharactersInOrder(topIds)
+    }
+
+    private fun loadCharactersInOrder(ids: List<Long>): List<ChatCharacter> {
+        if (ids.isEmpty()) return emptyList()
+        val list = chatCharacterRepository.findAllById(ids)
+        val map = list.associateBy { it.id }
+        return ids.mapNotNull { map[it] }
     }
 
     /**

src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/PopularCharacterQuery.kt

@@ -0,0 +1,54 @@
+package kr.co.vividnext.sodalive.chat.character.service
+
+import com.querydsl.jpa.impl.JPAQueryFactory
+import kr.co.vividnext.sodalive.chat.character.QChatCharacter
+import kr.co.vividnext.sodalive.chat.room.ParticipantType
+import kr.co.vividnext.sodalive.chat.room.QChatMessage
+import kr.co.vividnext.sodalive.chat.room.QChatParticipant
+import org.springframework.stereotype.Repository
+import java.time.Instant
+import java.time.LocalDateTime
+import java.time.ZoneOffset
+
+@Repository
+class PopularCharacterQuery(
+    private val queryFactory: JPAQueryFactory
+) {
+    /**
+     * 집계 기준: "채팅방 전체 메시지 수"로 캐릭터 인기 집계
+     * - 메시지 작성자(pMsg)가 누가 되었든 해당 방의 소유 캐릭터(p=CHARACTER)의 id로 그룹핑
+     * - 시간 종료 경계는 배타적(<) 비교로 단순화
+     */
+    fun findPopularCharacterIds(
+        windowStart: Instant,
+        endExclusive: Instant,
+        limit: Long
+    ): List<Long> {
+        val m = QChatMessage.chatMessage
+        val p = QChatParticipant.chatParticipant
+        val c = QChatCharacter.chatCharacter
+
+        val start = LocalDateTime.ofInstant(windowStart, ZoneOffset.UTC)
+        val end = LocalDateTime.ofInstant(endExclusive, ZoneOffset.UTC)
+
+        return queryFactory
+            .select(c.id)
+            .from(m)
+            // 방의 캐릭터 소유자 참가자(p=CHARACTER)를 통해 캐릭터 기준으로 그룹핑
+            .join(p).on(
+                p.chatRoom.id.eq(m.chatRoom.id)
+                    .and(p.participantType.eq(ParticipantType.CHARACTER))
+            )
+            .join(c).on(c.id.eq(p.character.id))
+            .where(
+                m.createdAt.goe(start)
+                    .and(m.createdAt.lt(end)) // 배타적 종료
+                    .and(m.isActive.isTrue)
+                    .and(c.isActive.isTrue)
+            )
+            .groupBy(c.id)
+            .orderBy(m.id.count().desc())
+            .limit(limit)
+            .fetch()
+    }
+}

src/main/kotlin/kr/co/vividnext/sodalive/chat/character/service/RankingWindowCalculator.kt

@@ -0,0 +1,37 @@
+package kr.co.vividnext.sodalive.chat.character.service
+
+import java.time.Instant
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.ZonedDateTime
+
+/**
+ * UTC 20:00:00을 경계로 집계 윈도우와 캐시 키를 계산한다.
+ */
+data class RankingWindow(
+    val windowStart: Instant,
+    val windowEnd: Instant,
+    val nextBoundary: Instant,
+    val cacheKey: String
+)
+
+object RankingWindowCalculator {
+    private val ZONE: ZoneId = ZoneOffset.UTC
+    private const val BOUNDARY_HOUR = 20 // 20:00:00 UTC
+
+    fun now(prefix: String = "popular-chat-character"): RankingWindow {
+        val now = ZonedDateTime.now(ZONE)
+        val todayBoundary = now.toLocalDate().atTime(BOUNDARY_HOUR, 0, 0).atZone(ZONE)
+        val (start, endExclusive, nextBoundary) = if (now.isBefore(todayBoundary)) {
+            val start = todayBoundary.minusDays(1)
+            Triple(start, todayBoundary, todayBoundary)
+        } else {
+            val next = todayBoundary.plusDays(1)
+            Triple(todayBoundary, next, next)
+        }
+        val windowStart = start.toInstant()
+        val windowEnd = endExclusive.minusNanos(1).toInstant() // [start, end]
+        val cacheKey = "$prefix:${windowStart.epochSecond}"
+        return RankingWindow(windowStart, windowEnd, nextBoundary.toInstant(), cacheKey)
+    }
+}

src/main/kotlin/kr/co/vividnext/sodalive/configs/RedisConfig.kt

@@ -123,6 +123,16 @@ class RedisConfig(
                 )
             )
 
+        // 24시간 TTL 캐시: 인기 캐릭터 집계용
+        cacheConfigMap["popularCharacters_24h"] = RedisCacheConfiguration.defaultCacheConfig()
+            .entryTtl(Duration.ofHours(24))
+            .serializeKeysWith(RedisSerializationContext.SerializationPair.fromSerializer(StringRedisSerializer()))
+            .serializeValuesWith(
+                RedisSerializationContext.SerializationPair.fromSerializer(
+                    GenericJackson2JsonRedisSerializer()
+                )
+            )
+
         return RedisCacheManager.builder(redisConnectionFactory)
             .cacheDefaults(defaultCacheConfig)
             .withInitialCacheConfigurations(cacheConfigMap)