Android Dropbox api文件存在

Question

I'm downloading a file from Dropbox successfully, but now I want to check if the file in Dropbox does not exist.
It seems that the FileNotFoundException does not work, so I added a boolean to check this, but without success.
Do you have any advice?

 protected class DownloadDB extends AsyncTask<Context, Integer, String> {
    ProgressDialog myLoadingDialog;
    boolean exists = true;
     @Override
    protected void onPreExecute() {
        myLoadingDialog = new ProgressDialog(Impostazioni_pro.this);
        myLoadingDialog.setMessage(getString(R.string.sinc));
        myLoadingDialog.setIndeterminate(false);
        myLoadingDialog.setCancelable(false);
        myLoadingDialog.show();
        super.onPreExecute();
    }

    @Override
    protected String doInBackground(Context... arg0) {

        try {
            File OutFolder = new File(Environment.getExternalStorageDirectory(), getString(R.string.app_name) + "/sync/psw.crypt");
            OutputStream out = new FileOutputStream(OutFolder);
            mApi.getFile("/myfile.db", null, out, null);
        } catch (FileNotFoundException e) {
            exists = false;
            e.printStackTrace();
         } catch (DropboxException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        myLoadingDialog.dismiss();
            if(exists){

                importaDB();
            }
        super.onPostExecute(result);
    }
}

Answer 1

Try catching just the generic Exception:

    try {
        File OutFolder = new File(Environment.getExternalStorageDirectory(), getString(R.string.app_name) + "/sync/psw.crypt");
        OutputStream out = new FileOutputStream(OutFolder);
        mApi.getFile("/myfile.db", null, out, null);
    } catch (Exception e) {
        exists = false;
        e.printStackTrace();
    }

Answer 2

I use DbxException message:

try{
    OutputStream outputStream = new FileOutputStream(dbPath);
    client.files.downloadBuilder("/"+backupFileName).run(outputStream);
} catch (DbxException e) {
    if (e.getMessage().contains("not_found")) exists= false;
}