This is the code I am using to download a file from a URL. How can I optimize this code, or is there another way to download a file faster? And how much should the value of the BUFFER_SIZE be?

private final int BUFFER_SIZE = 4096; public String downloadFile(String fileURL, String saveDir) throws IOException {      URL url = new URL(fileURL);     HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();     int responseCode = httpConn.getResponseCode();      if (responseCode == HttpURLConnection.HTTP_OK) {         String fileName = "";         String disposition = httpConn.getHeaderField("Content-Disposition");          if (disposition != null) {             int index = disposition.indexOf("filename=");             if (index > 0) {                 fileName = disposition.substring(index + 10,                     disposition.length() - 1);             }         } else {             fileName = fileURL.substring(fileURL.lastIndexOf("/") + 1,                 fileURL.length());         }          InputStream inputStream = httpConn.getInputStream();         String saveFilePath = saveDir + File.separator + fileName;          FileOutputStream outputStream = new FileOutputStream(saveFilePath);          int bytesRead = -1;         byte[] buffer = new byte[BUFFER_SIZE];         while ((bytesRead = inputStream.read(buffer)) != -1) {             outputStream.write(buffer, 0, bytesRead);         }          outputStream.close();         inputStream.close();          return saveFilePath;     }     httpConn.disconnect();     return null; }