code: @Override
      public void close() {
          ComboException ce = new ComboException();
          for (ConnInfo cInfo : list) {
              try {
                  // 试图恢复旧的事务级别
                  if (!cInfo.conn.isClosed()) {
                      if (cInfo.restoreIsoLevel)
                          cInfo.conn.setTransactionIsolation(cInfo.oldLevel);
                      if (cInfo.restoreAutoCommit)
                          cInfo.conn.setAutoCommit(true);
                  }
              }
              catch (Throwable e) {}
              finally {
                  try {
                      cInfo.conn.close();
                  }
                  catch (Exception e) {
                      ce.add(e);
                  }
              }
          }
          // 清除数据源记录
          list.clear();
      }
docs: 关闭事务,清理现场