perf(#111): 조회하려는 file이 null일 경우 null 반환

- 존재하지 않는 파일에 대해서도 presigned url이 생성되는 것을 방지하기 위해 파일이 존재하지 않으면 null을 반환하도록 변경했습니다.

src/main/java/com/bamdoliro/maru/infrastructure/s3/UploadFileService.java

@@ -4,10 +4,7 @@
 import com.amazonaws.SdkClientException;
 import com.amazonaws.services.s3.AmazonS3Client;
 import com.amazonaws.services.s3.Headers;
-import com.amazonaws.services.s3.model.CannedAccessControlList;
-import com.amazonaws.services.s3.model.GeneratePresignedUrlRequest;
-import com.amazonaws.services.s3.model.ObjectMetadata;
-import com.amazonaws.services.s3.model.PutObjectRequest;
+import com.amazonaws.services.s3.model.*;
 import com.bamdoliro.maru.infrastructure.s3.dto.response.UploadResponse;
 import com.bamdoliro.maru.infrastructure.s3.exception.FailedToSaveException;
 import com.bamdoliro.maru.infrastructure.s3.validator.FileValidator;
@@ -66,7 +63,7 @@ public UploadResponse getDownloadPresignedUrl(String folder, String fileName) {
         GeneratePresignedUrlRequest request = getGenerateDownloadPresignedUrlRequest(bucket, fullFileName);
 
         return new UploadResponse(
-                amazonS3Client.generatePresignedUrl(request).toString()
+                request != null ? amazonS3Client.generatePresignedUrl(request).toString() : null
         );
     }
 
@@ -77,10 +74,18 @@ private GeneratePresignedUrlRequest getGenerateUploadPresignedUrlRequest(String
     }
 
     private GeneratePresignedUrlRequest getGenerateDownloadPresignedUrlRequest(String bucket, String fileName) {
-
-        return new GeneratePresignedUrlRequest(bucket, fileName)
-                .withMethod(HttpMethod.GET)
-                .withExpiration(getPresignedUrlExpiration(60 * 10));
+        try {
+            amazonS3Client.getObjectMetadata(bucket, fileName);
+
+            return new GeneratePresignedUrlRequest(bucket, fileName)
+                    .withMethod(HttpMethod.GET)
+                    .withExpiration(getPresignedUrlExpiration(60 * 10));
+        } catch (AmazonS3Exception e) {
+            if (e.getStatusCode() == 404) {
+                return null;
+            }
+            throw e;
+        }
     }
 
     private Date getPresignedUrlExpiration(int duration) {