jdbc 程序回顾

public static void main(String[] args) {
    Connection connection = null;
    PreparedStatement preparedStatement = null;
    ResultSet resultSet = null;
    try{
        Class.forName("com.mysql.jdbc.Driver");
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis","root","liao1024");
        String sql = "select * from user";
        preparedStatement = connection.prepareStatement(sql);
        resultSet = preparedStatement.executeQuery();
        while(resultSet.next()){
            System.out.println(resultSet);
        }
    }catch (Exception e){
        e.printStackTrace();
    }finally {
        if (resultSet!=null){
            try{
            resultSet.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
        if (preparedStatement!=null){
            try{
                preparedStatement.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
        if (connection!=null){
            try{
                connection.close();
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
    }
}
缺点:
1.数据库链接创建,释放频繁造成系统资源浪费从而影响系统性能--->使用数据库连接池
2.sql语句的变动需要改变源代码, 不符合开发的开闭原则,系统不易维护
3.对结果集(ResultSet)查询列名,如果能将数据封装为实体类解析更加方便