I get an error open failed: EROFS (Read-only file system), how to fix it?

Question

Java

I'm trying to save the downloaded file and I get - java.io.FileNotFoundException: /1.gif: open failed: EROFS (Read-only file system)
How did you fix it??
marked in the code where the error occurs.

private String saveFilePatch = "/1.gif";
    private ProgressDialog dialog = null;
    private String urlFile="https://vk.com/doc430279622_445877224?hash=d20c78fff02c29f267&dl=GQZTAMRXHE3DEMQ:1496394942:6d9c703cd7409eda1b&api=1&no_preview=1";

    private void downloadFile(String url, String saveFilePatch){
        try {
            File SaveFile = new File(saveFilePatch);
            URL u = new URL(url);
            URLConnection con = u.openConnection();
            int lengthofContext = con.getContentLength();

            DataInputStream dataInputStream = new DataInputStream(u.openStream());
            byte[] buffer = new byte[lengthofContext];
            dataInputStream.readFully(buffer);
            dataInputStream.close();

            FileOutputStream fos = new FileOutputStream(SaveFile);
          <b>  // ошибка выпадает в этой строке</b>
            DataOutputStream dataOutputStream = new DataOutputStream(fos);

            dataOutputStream.write(buffer);
            dataOutputStream.flush();
            dataOutputStream.close();
            fos.close();
            hideProgressIndicator();

        }catch (IOException e){
            hideProgressIndicator();
            e.printStackTrace();
        }
        catch (Exception e){
            e.printStackTrace();
        }
    }

    private void hideProgressIndicator() {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                dialog.dismiss();
            }
        });
    }

    public void onClickBtnTwo(View view) {
        if (urlFile != "") {
            dialog = ProgressDialog.show(MainActivity.this, "", "Download...", true);
            new Thread(new Runnable() {
                @Override
                public void run() {
                    downloadFile(urlFile, saveFilePatch);
                }
            }).start();
        }else {
            System.out.println("null photo");
        }
    }

в манифесте прописано
    <uses-permission android:name="android.permission.INTERNET"></uses-permission>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />