Returning a MultipartFile directly in a Spring Boot response will not work as you expect because MultipartFile is not a serializable object, and Spring attempts to serialize it into JSON.

Instead, you can stream the file content directly in the response. Here’s how you can do it:

Change the Return Type: Instead of returning a MultipartFile, return a ResponseEntity with the byte array of the file or an InputStream. Set the Appropriate Headers: Ensure you set the correct content type and any other necessary headers.

@RestController public class YourController {

@GetMapping("/your-endpoint")
public ResponseEntity<InputStreamResource> getFile() {
    // Simulating your image upload response
    ImageUploadResponse imageUploadResponse = ...; // Get your imageUploadResponse

    InputStream inputStream = imageUploadResponse.getInputStream();
    String fileName = imageUploadResponse.getKey();
    String mimeType = imageUploadResponse.getMimeType();

    HttpHeaders headers = new HttpHeaders();
    headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + fileName);
    headers.add(HttpHeaders.CONTENT_TYPE, mimeType);

    InputStreamResource resource = new InputStreamResource(inputStream);

    return new ResponseEntity<>(resource, headers, HttpStatus.OK);
}

}

Explanation: InputStreamResource: This allows you to send an InputStream as a response body, which is suitable for file downloads. Headers: You can set headers such as Content-Disposition to specify how the file should be handled by the client (download, inline, etc.). Content-Type: Make sure you set the correct MIME type for the file.