/**
* 参数：表名
*/
public List<Map<String, Object>> getMetaData(String tableName){
        Connection connection = null;
        List<String> columnNames = new ArrayList<>();
        List<Map<String, Object>> dataList = new ArrayList<>();
        try {
            connection = dataSource.getConnection();
            String sql = "select * from " + tableName;
            Statement statement = connection.createStatement();
            ResultSet resultSet = statement.executeQuery(sql);
            //关键一步：根据结果集获取元数据
            ResultSetMetaData metaData = resultSet.getMetaData();
            //获取表中的列数
            int columnCount = metaData.getColumnCount();
            for (int i=1; i<=columnCount; i++){
                //获取所有列名
                columnNames.add(metaData.getColumnName(i));
            }
            while (resultSet.next()){
                Map<String, Object> columnData = new HashMap<>();
                //根据所有列名，获取所有数据
                for (String columnName : columnNames){
                    Object object = resultSet.getObject(columnName);
                    columnData.put(columnName, object);
                }
                dataList.add(columnData);
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
        return dataList;
    }