static String getDataSource() {
    Properties props = new Properties();
    try {
      props.load(new InputStreamReader(new FileInputStream("pos.properties"), "UTF-8"));
    } catch (UnsupportedEncodingException e) {
      throw new RuntimeException(e);
    } catch (FileNotFoundException e) {
      throw new RuntimeException("jarファイルと同じディレクトリに pos.properties を配置してください。");
    } catch (IOException e) {
      throw new RuntimeException(e);
    }

    return props.getProperty("datasource");
  }