在公共添加文件夹中的内部存储？(Adding folder in Internal Storage

我创建Excel文件，将其存储在内部存储，但我不能只do.It应用存储directory.Not可见在public.How创建文件夹，存储文件夹中的文件中创建？任何人都可以知道一个帮我解决这个问题。

创建文件编码

 public String generate(String file_name,String path) {

    try {

        f = new File(activity.getFilesDir(), path);
        if (!f.exists()) {
           f.mkdirs();
        }


        file = new File(f.getAbsolutePath(), file_name);
        if (file.createNewFile()) {
            file.createNewFile();
        }

        wb_setting = new WorkbookSettings();
        wb_setting.setLocale(new Locale("en", "EN"));

        workbook = Workbook.createWorkbook(file, wb_setting);
        workbook.createSheet("Report", 0);
        excelSheet = workbook.getSheet(0);
        createLabel(excelSheet);
        createContent(excelSheet);

        workbook.write();
        workbook.close();

        file_path_alert_builder = new AlertDialog.Builder(activity);
        file_path_alert_builder.setTitle("File path");
        file_path_alert_builder.setMessage(""+file).setCancelable(true).setPositiveButton("OK",new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialogInterface, int i) {

                dialogInterface.dismiss();

            }
        });

        file_path_dialog = file_path_alert_builder.create();
        file_path_dialog.show();
    }catch (JXLException jxl_e) {
        jxl_e.printStackTrace();
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return null;
}