refactor: refact pagination code

common/src/main/java/com/oing/util/Paginator.java

@@ -0,0 +1,38 @@
+package com.oing.util;
+
+import com.oing.domain.PaginationDTO;
+
+import java.util.Collections;
+import java.util.List;
+
+public class Paginator<T> {
+    private final List<T> items;
+    private final int pageSize;
+
+    public Paginator(List<T> items, int pageSize) {
+        if (pageSize <= 0) {
+            throw new IllegalArgumentException("Page size must be greater than 0.");
+        }
+        this.items = items != null ? items : Collections.emptyList();
+        this.pageSize = pageSize;
+    }
+
+    public PaginationDTO<T> getPage(int pageNumber) {
+        if (pageNumber <= 0) {
+            throw new IllegalArgumentException("Page number must be greater than 0.");
+        }
+
+        int totalItems = items.size();
+        int totalPages = (int) Math.ceil((double) totalItems / pageSize);
+
+        if (pageNumber > totalPages) {
+            return new PaginationDTO<>(totalPages, Collections.emptyList());
+        }
+
+        int startIndex = (pageNumber - 1) * pageSize;
+        int endIndex = Math.min(startIndex + pageSize, totalItems);
+
+        List<T> pageItems = items.subList(startIndex, endIndex);
+        return new PaginationDTO<>(totalPages, pageItems);
+    }
+}

post/src/main/java/com/oing/controller/CommentController.java

@@ -13,14 +13,14 @@
 import com.oing.service.MemberBridge;
 import com.oing.service.PostService;
 import com.oing.service.VoiceCommentService;
+import com.oing.util.Paginator;
 import jakarta.transaction.Transactional;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Controller;
 
 import java.time.ZoneId;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
 
@@ -142,21 +142,8 @@ private Comparator<PostCommentResponseV2> getCommentComparator(String sort) {
     }
 
     private PaginationResponse<PostCommentResponseV2> paginateComments(List<PostCommentResponseV2> comments, Integer page, Integer size) {
-        int total = comments.size();
-        int totalPage = (int) Math.ceil((double) total / size);
-        if (page > totalPage) {
-            // 데이터가 없는 페이지 요청 시 빈 목록 반환
-            return PaginationResponse.of(
-                    new PaginationDTO<>(totalPage, Collections.emptyList()),
-                    page,
-                    size
-            );
-        }
-
-        int start = (page - 1) * size;
-        int end = Math.min(start + size, total);
-        List<PostCommentResponseV2> paginatedComments = comments.subList(start, end);
-        PaginationDTO<PostCommentResponseV2> paginationDTO = new PaginationDTO<>(totalPage, paginatedComments);
+        Paginator<PostCommentResponseV2> paginator = new Paginator<>(comments, size);
+        PaginationDTO<PostCommentResponseV2> paginationDTO = paginator.getPage(page);
 
         return PaginationResponse.of(paginationDTO, page, size);
     }