code: public static void closeConnectionAuto(Connection conn) {
          if (get() == null && null != conn) {
              try {
                  conn.close();
              }
              catch (SQLException e) {
                  throw Lang.wrapThrow(e);
              }
          }
      }
docs: 自动判断是否关闭当前连接
  @param conn 数据库连接