How to return both JSON response and Byte Array of file in Springboot RestController Response while downloading a file

Question

I am developing a rest controller to download a.docx file into the client system. My code is working fine as the file is getting downloaded. Now I want to enhance the response. My requirement is to also send a JSON payload in the response along with the.docx file content, something like

{"message":"Report downloaded Successfully"}

incase of successful download or with a different message incase of failure.

Below is my restcontroller code:

@RestController
public class DownloadController {
    
    
    @PostMapping(value="/download",
            consumes = {"multipart/form-data"},
            produces = {"application/octet-stream"})
    public ResponseEntity<?> downloadFile(@RequestParam("file") MultipartFile uploadFile){
        
        //business logic to create the attachment file
        
        try {
            
            File file = new File("path_to_.DOCX file_I_have_created");
            byte[] contents = Files.readAllBytes(Paths.get(file.getAbsolutePath()));
            
            HttpHeaders headers = new HttpHeaders();
            headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
            headers.setContentDisposition(ContentDisposition.attachment().filename("survey.docx").build());
            
            return new ResponseEntity<>(contents, headers, HttpStatus.OK);
        } catch (Exception e){
            return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
        }
    }

}

How do I modify my response code to send both the JSON message and the byte[] contents so that the file gets downloaded and I can see the JSON message in the response preview tab in the chrome or response body in postman?

Answer 1

You can't. HTTP doesn't allow you to defined multiple content-types on 1 request/response. That being said, you could send the byte array base64 encoded as part of a json response but would need to handle it in the front-end (if you have any) as it would not trigger the file download process of the browser.

Answer 2

You can define custom class which hold your current content and message. So you can return that class in the response

ResponseClass
{
byte[] contents;
String message;
}