if (Files.exists(file)) {
            response.setContentType(existingDocuments.getContentType());
            response.addHeader("Content-Disposition", "attachment; filename=" + existingDocuments.getFileName());
            Files.copy(file, response.getOutputStream());
            response.getOutputStream().flush();
        }

String filePath=request.getParameter("filepath");
    File file=new File(filePath);
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition",
    "attachment;filename="+file.getName());
    InputStream is=new FileInputStream(file);
    int read=0;
    byte[] bytes = new byte[256];
    OutputStream os = response.getOutputStream();
    while((read = is.read(bytes))!= -1){
     os.write(bytes, 0, read);
    }

    os.flush();
    is.close();
    os.close();

response.header("content-disposition", "attachment; filename="" + fileNameDisplay + """);