[Refactor] 메인 페이지 API 개선 - 팔로우 여부 확인, userId 추가, 카테고리 정렬

src/main/java/org/example/studylog/controller/MainController.java

@@ -47,7 +47,8 @@ public class MainController {
                                             + "\"data\": {"
                                             + "\"following\": [],"
                                             + "\"profile\": {"
-                                            + "\"coverImage\": \"https://example.com/bg.jpg\","
+                                            + "\"userId\": 1,"
+                                            + "\"coverImage\": null,"
                                             + "\"profileImage\": \"https://example.com/profile.jpg\","
                                             + "\"name\": \"홍길동\","
                                             + "\"intro\": \"안녕하세요! 개발 공부 중입니다.\","

src/main/java/org/example/studylog/dto/MainPageResponseDTO.java

@@ -26,6 +26,7 @@ public class MainPageResponseDTO {
     @NoArgsConstructor
     @AllArgsConstructor
     public static class ProfileDTO {
+        private Long userId;
         private String coverImage;
         private String profileImage;
         private String name;

src/main/java/org/example/studylog/service/MainService.java

@@ -45,7 +45,8 @@ public MainPageResponseDTO getMainPageData(User user) {
 
         // 2. 프로필 정보 생성
         MainPageResponseDTO.ProfileDTO profile = MainPageResponseDTO.ProfileDTO.builder()
-                .coverImage(user.getBackImage() != null ? user.getBackImage() : "https://example.com/bg.jpg")
+                .userId(user.getId())
+                .coverImage(user.getBackImage())  // null이면 null 반환
                 .profileImage(user.getProfileImage())
                 .name(user.getNickname())
                 .intro(user.getIntro())
@@ -123,6 +124,7 @@ private List<MainPageResponseDTO.CategoryCountDTO> getCategoryCountData(User use
                         .name(category.getName())
                         .count(categoryCountMap.getOrDefault(category.getId(), 0))
                         .build())
+                .sorted((a, b) -> b.getCount().compareTo(a.getCount()))  // count 기준 내림차순 정렬
                 .toList();
     }
 
@@ -135,7 +137,8 @@ public MainPageResponseDTO getMainPageDataWithFollowStatus(User targetUser, User
         List<FriendResponseDTO> following = friendRepositoryImpl.findFriendListByUser(targetUser);
 
         MainPageResponseDTO.ProfileDTO profile = MainPageResponseDTO.ProfileDTO.builder()
-                .coverImage(targetUser.getBackImage() != null ? targetUser.getBackImage() : "https://example.com/bg.jpg")
+                .userId(targetUser.getId())
+                .coverImage(targetUser.getBackImage())  // null이면 null 반환
                 .profileImage(targetUser.getProfileImage())
                 .name(targetUser.getNickname())
                 .intro(targetUser.getIntro())