fix(file-service): stream upload to disk to fix OOM on large files

file.getBytes() loaded the entire APK into JVM heap, causing
OutOfMemoryError on files >~50MB. Now streams to a temp file while
computing SHA-256 via DigestInputStream, then atomically moves to the
final path. Zero heap cost regardless of file size.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

file-service/src/main/java/com/xuqm/file/service/FileStorageService.java

@@ -14,11 +14,14 @@ import org.springframework.web.multipart.MultipartFile;
 import javax.imageio.ImageIO;
 import java.awt.*;
 import java.awt.image.BufferedImage;
-import java.io.ByteArrayInputStream;
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.nio.file.StandardCopyOption;
+import java.security.DigestInputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.time.Instant;
@@ -62,39 +65,49 @@ public class FileStorageService {
             throw new BusinessException(400, "File must not be empty");
         }
 
-        byte[] bytes;
+        String originalName = file.getOriginalFilename();
+        String mimeType = resolveMimeType(file);
+        String ext = resolveExtension(originalName, mimeType);
+
+        Path storageDir = Paths.get(uploadDir);
+        ensureDirectory(storageDir);
+
+        // Stream to a temp file while computing SHA-256 to avoid loading the whole file into heap
+        Path tempPath = storageDir.resolve("tmp-" + UUID.randomUUID() + ".tmp");
+        String hash;
+        long fileSize;
         try {
-            bytes = file.getBytes();
-        } catch (IOException e) {
+            MessageDigest digest = MessageDigest.getInstance("SHA-256");
+            try (InputStream in = new DigestInputStream(file.getInputStream(), digest);
+                 OutputStream out = Files.newOutputStream(tempPath)) {
+                fileSize = in.transferTo(out);
+            }
+            hash = HexFormat.of().formatHex(digest.digest());
+        } catch (IOException | NoSuchAlgorithmException e) {
+            try { Files.deleteIfExists(tempPath); } catch (IOException ignored) {}
             throw new BusinessException(500, "Failed to read uploaded file");
         }
 
-        String hash = sha256Hex(bytes);
-        String mimeType = resolveMimeType(file);
-        String originalName = file.getOriginalFilename();
-
         Optional<FileEntity> existing = fileRepository.findByHash(hash);
         if (existing.isPresent()) {
             FileEntity entity = existing.get();
-            // 检查磁盘文件是否仍然存在，若不存在则重新写入
             if (Files.exists(Paths.get(entity.getStoragePath()))) {
+                // File already on disk — drop temp and return existing record
+                try { Files.deleteIfExists(tempPath); } catch (IOException ignored) {}
                 entity.setLastAccessedAt(Instant.now());
                 fileRepository.save(entity);
                 return toUploadResult(entity);
             }
-            // 文件记录存在但磁盘文件已丢失，删除旧记录后重新上传
+            // 文件记录存在但磁盘文件已丢失，删除旧记录，保留 temp 继续写入
             fileRepository.delete(entity);
             fileRepository.flush();
         }
 
-        String ext = resolveExtension(originalName, mimeType);
-        Path storageDir = Paths.get(uploadDir);
-        ensureDirectory(storageDir);
-
         Path storagePath = storageDir.resolve(hash + ext);
         try {
-            Files.write(storagePath, bytes);
+            Files.move(tempPath, storagePath, StandardCopyOption.REPLACE_EXISTING);
         } catch (IOException e) {
+            try { Files.deleteIfExists(tempPath); } catch (IOException ignored) {}
             throw new BusinessException(500, "Failed to save uploaded file");
         }
 
@@ -111,7 +124,7 @@ public class FileStorageService {
                 }
             }
         } else if (mimeType != null && mimeType.startsWith("image/")) {
-            thumbnailStoragePath = generateImageThumbnail(bytes, hash);
+            thumbnailStoragePath = generateImageThumbnail(storagePath, hash);
             if (thumbnailStoragePath != null) {
                 try {
                     thumbnailSize = Files.size(Paths.get(thumbnailStoragePath));
@@ -127,7 +140,7 @@ public class FileStorageService {
         entity.setHash(hash);
         entity.setOriginalName(originalName);
         entity.setMimeType(mimeType);
-        entity.setSize(bytes.length);
+        entity.setSize(fileSize);
         entity.setExt(ext);
         entity.setStoragePath(storagePath.toAbsolutePath().toString());
         entity.setThumbnailPath(thumbnailStoragePath);
@@ -193,9 +206,9 @@ public class FileStorageService {
         }
     }
 
-    private String generateImageThumbnail(byte[] imageBytes, String hash) {
+    private String generateImageThumbnail(Path imagePath, String hash) {
         try {
-            BufferedImage original = ImageIO.read(new ByteArrayInputStream(imageBytes));
+            BufferedImage original = ImageIO.read(imagePath.toFile());
             if (original == null) {
                 return null;
             }
@@ -230,16 +243,6 @@ public class FileStorageService {
         }
     }
 
-    private String sha256Hex(byte[] data) {
-        try {
-            MessageDigest digest = MessageDigest.getInstance("SHA-256");
-            byte[] hashBytes = digest.digest(data);
-            return HexFormat.of().formatHex(hashBytes);
-        } catch (NoSuchAlgorithmException e) {
-            throw new IllegalStateException("SHA-256 not available", e);
-        }
-    }
-
     private String resolveMimeType(MultipartFile file) {
         String ct = file.getContentType();
         if (ct != null && !ct.isBlank() && !ct.equals("application/octet-stream")) {