FirebaseFileDownload.java

    
    @Override
    public ResponseEntity<Object> downloadFile(String fileName, HttpServletRequest request) throws Exception {
        Storage storage = storageOptions.getService();

        Blob blob = storage.get(BlobId.of(bucketName, fileName));
        ReadChannel reader = blob.reader();
        InputStream inputStream = Channels.newInputStream(reader);

        byte[] content = null;
        log.info("File downloaded successfully.");

        content = IOUtils.toByteArray(inputStream);

        final ByteArrayResource byteArrayResource = new ByteArrayResource(content);

        return ResponseEntity
                .ok()
                .contentLength(content.length)
                .header("Content-type", "application/octet-stream")
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + fileName + "\"")
                .body(byteArrayResource);

    }