KKUMI-118 [FEATURE] #73 포스트 좋아요 개수 조회 + 좋아요 Redis 캐싱

포스트에 좋아요 개수를 조회하는 부분 구현, 한번 조회됐던 좋아요개수는 30초간 캐싱되도록 함
흐름은 아래와 같습니다.
1. Redis에서 post의 좋아요 개수 조회
2-1. Redis에 존재하면 바로 리턴
2-2. Redis에 존재하지 않으면 DB에서 조회 후 PostLikeCountCacheMissEvent 발생시켜 Redis에 캐싱되도록 함

src/main/java/com/swmarastro/mykkumiserver/like/LikesRepository.java

@@ -23,4 +23,8 @@ public interface LikesRepository extends JpaRepository<Likes, Long> {
             "LEFT JOIN likes l ON p.post_id = l.post_id AND l.user_id = :userId " +
             "WHERE p.post_id IN :postIds", nativeQuery = true)
     List<Map<String, Object>> findPostLikesStatus(List<Long> postIds, Long userId);
+
+    @Query(value = "SELECT COUNT(l) FROM Likes l " +
+        "WHERE l.post.id = :postId AND l.isDeleted = false")
+    Long findPostLikeCountByPostId(Long postId);
 }

src/main/java/com/swmarastro/mykkumiserver/like/LikesService.java

@@ -2,10 +2,13 @@
 
 import com.swmarastro.mykkumiserver.global.exception.CommonException;
 import com.swmarastro.mykkumiserver.global.exception.ErrorCode;
+import com.swmarastro.mykkumiserver.global.util.RedisUtils;
 import com.swmarastro.mykkumiserver.post.PostRepository;
 import com.swmarastro.mykkumiserver.post.domain.Post;
+import com.swmarastro.mykkumiserver.post.event.PostLikeCountCacheMissEvent;
 import com.swmarastro.mykkumiserver.user.User;
 import lombok.RequiredArgsConstructor;
+import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 
@@ -21,6 +24,11 @@ public class LikesService {
 
     private final LikesRepository likeRepository;
     private final PostRepository postRepository;
+    private final RedisUtils redisUtils;
+    private final ApplicationEventPublisher eventPublisher;
+
+    private static final String POST_LIKE_KEY_PREFIX = "post:";
+    private static final String POST_LIKE_KEY_SUFFIX = ":likes";
 
     public Boolean like(User user, Long postId) {
 
@@ -50,7 +58,7 @@ public Boolean unlike(User user, Long postId) {
         Optional<Likes> optionalLike = likeRepository.findByPostAndUser(post, user);
 
         //없음 -> 좋아요를 취소할 수 없습니다.
-        if(optionalLike.isEmpty()) {
+        if (optionalLike.isEmpty()) {
             //TODO 이게 not_found가 맞는지 뭘쓸지 모르겠다
             throw new CommonException(ErrorCode.NOT_FOUND, "좋아요를 취소할 수 없습니다.", "좋아요를 취소할 수 없습니다.");
         }
@@ -73,4 +81,21 @@ public List<Boolean> isLikedByUser(User user, List<Long> postIds) {
                 .map(postId -> likeStatusMap.getOrDefault(postId, false))
                 .collect(Collectors.toList());
     }
+
+    public Long getPostLikeCount(Long postId) {
+        Long value = redisUtils.getLongValues(makePostLikeKey(postId));
+        if (value != null) {
+            return value;
+        }
+        //없으면 DB에서 조회
+        Long postLikeCount = likeRepository.findPostLikeCountByPostId(postId);
+        //redis 갱신하도록 이벤트 던지기
+        eventPublisher.publishEvent(new PostLikeCountCacheMissEvent(postId, postLikeCount));
+        return postLikeCount;
+    }
+
+    private String makePostLikeKey(Long postId) {
+        return POST_LIKE_KEY_PREFIX + postId + POST_LIKE_KEY_SUFFIX;
+    }
+
 }

src/main/java/com/swmarastro/mykkumiserver/post/event/PostLikeCountCacheMissEvent.java

@@ -0,0 +1,12 @@
+package com.swmarastro.mykkumiserver.post.event;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+
+@Getter
+@AllArgsConstructor
+public class PostLikeCountCacheMissEvent {
+
+    private final Long postId;
+    private final Long likeCount;
+}

src/main/java/com/swmarastro/mykkumiserver/post/event/listener/PostLikeEventListener.java

@@ -0,0 +1,33 @@
+package com.swmarastro.mykkumiserver.post.event.listener;
+
+import com.swmarastro.mykkumiserver.global.util.RedisUtils;
+import com.swmarastro.mykkumiserver.post.event.PostLikeCountCacheMissEvent;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.context.event.EventListener;
+import org.springframework.scheduling.annotation.Async;
+import org.springframework.stereotype.Component;
+
+import java.time.Duration;
+
+@Slf4j
+@Component
+@RequiredArgsConstructor
+public class PostLikeEventListener {
+
+    private final RedisUtils redisUtils;
+    private static final String POST_LIKE_KEY_PREFIX = "post:";
+    private static final String POST_LIKE_KEY_SUFFIX = ":likes";
+    private static final Duration POST_LIKE_DURATION = Duration.ofSeconds(30);
+
+    @Async
+    @EventListener
+    public void setPostLikeCountCache(PostLikeCountCacheMissEvent postLikeCountCacheMissEvent) {
+        String key = makePostLikeKey(postLikeCountCacheMissEvent.getPostId());
+        redisUtils.setValues(key, postLikeCountCacheMissEvent.getLikeCount(), POST_LIKE_DURATION);
+    }
+
+    private String makePostLikeKey(Long postId) {
+        return POST_LIKE_KEY_PREFIX + postId + POST_LIKE_KEY_SUFFIX;
+    }
+}