Eine URL mit Hilfe von GridFS DownloadToStream ersetzen

  // Obtain asset DATA url
    public String obtainFileUrl(GridFSBucket bucket, String fileNameOrId) {
        // open download stream
        GridFSDownloadStream downloadStream = bucket.openDownloadStream(fileNameOrId);
        // get file info, we need content type and file size
        GridFSFile file = downloadStream.getGridFSFile();
        // get content type
        org.bson.Document metadata = file.getMetadata();
        // if content type of asset is not stored as this key, change it
        String contentType = metadata.getString("contentType");
        // create byte buffer to read our stream
       // this can be bad if files are too big or memory is limited so be careful 
        byte[] raw = new byte[(int)file.getLength()];
        downloadStream.read(raw);
        downloadStream.close();
        // encode asset raw bytes to base64 string
        String base64EncodedAsset = Base64.getEncoder().encodeToString(raw);
        // create data url
        String url = String.format("data:%s;base64,%s", contentType, base64EncodedAsset);
        return url;
    }

GridFSDownloadStream downloadStream = bucket.openDownloadStream(fileNameOrId);

{
...
 try {

    InputStream is = downloadStream;
     response.setContentType(contentType);      
     response.setHeader("Content-Disposition", "attachment;filename=\"+file.getFilename​()+\""); 
     // copy it to response's OutputStream
      org.apache.commons.io.IOUtils.copy(is, response.getOutputStream());
      response.flushBuffer();
    } catch (IOException ex) {
      throw new RuntimeException("IOError writing file to output stream");
    }