// HttpServletRequest request
Part part = request.getPart("file");
String fileName = part.getSubmittedFileName();
File file = new File("files/" + fileName);
InputStream inputStream = part.getInputStream();
byte[] buffer = new byte[1024];
try (OutputStream outputStream = new FileOutputStream(file)) {
    while (true) {
        int read = inputStream.read(buffer);
        if (read > 0) {
            outputStream.write(buffer, 0, read);
        } else {
            break;
        }
    }
}