手写MyBatis框架

原生JDBC

框架写法

测试

源码地址

---

手写Mybatis框架更有利于了解框架底层，做到知其然知其所以然。

原生JDBC

/**
 * 原生jdbc写法
 *
 * @author lipangpang
 * @date 2022/3/13
 * @description
 */
public class JdbcDemo {
    public static void main(String[] args) {
        MallUser user = new MallUser();
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&serverTimezone=Asia/Shanghai", "root", "123456");
            String sql = "select * from mall_user where name = ?";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, "张三");
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                Long id = resultSet.getLong("id");
                String username = resultSet.getString("name");
                user.setId(id);
                user.setName(username);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (resultSet != null) {
                try {
                    resultSet.close();
                } catch (SQLException sqlException) {
                    sqlException.printStackTrace();
                }
            }
            if (preparedStatement != null) {
                try {
                    preparedStatement.close();
                } catch (SQLException sqlException) {
                    sqlException.printStackTrace();
                }
            }
            if (connection != null) {
                try {
                    connection.close();
                } catch (SQLException sqlException) {
                    sqlException.printStackTrace();
                }
            }
        }
        System.out.println(user);
    }
}

原生JDBC写法的弊端有：

1. 数据库配置信息及sql语句硬编码。
2. 重复创建和关闭数据库连接。

框架写法

此处文件的命名参考MyBatis源码命名风格，有利于后续查看源码。

工程结构如下：

表结构如下：

框架大致流程如下：

1. 创建mapper.xml文件用来存储sql查询语句，创建sqlMapConfig.xml来存储数据库配置信息和mapper.xml文件所在路径。

   sqlMapConfig.xml
   
       
           
           
           
           
       
   
       
       
   
   
   MallUserMapper.xml
   
       
           select * from mall_user
       
       
           select * from mall_user where id = #{id} and name = #{name}
       
       
           insert into mall_user(name) values(#{name})
       
   
   
   MallRoleMapper.xml
   
       
           select * from mall_role
       
       
           select * from mall_role where id = #{id} and name = #{name}
       
       
           insert into mall_role(name) values(#{name})
       
   

2. 按照面向对象编程思想，将第一步解析出来的内容分别封装到MappedStatement和Configuration实体类中。

   /**
    * 配置文件对象
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   @Data
   public class Configuration {
       private DataSource dataSource;
       //key:命名空间+id
       private Map mappedStatementMap = new HashMap<>();
   }
   
   /**
    * mapper配置文件对象
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   @Data
   public class MappedStatement {
       /**
        * 标识
        */
       private String id;
       /**
        * 返回结果类型
        */
       private String resultType;
       /**
        * 参数查询类型
        */
       private String parameterType;
       /**
        * sql语句
        */
       private String sql;
   
   }

3. 通过SqlSessionFactoryBuilder构建者创建SqlSessionFactory。

   /**
    * SqlSessionFactory构建者
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   public class SqlSessionFactoryBuilder {
       /**
        * 构建
        *
        * @param inputStream 文件配置流
        * @return
        * @throws PropertyVetoException
        * @throws DocumentException
        */
       public SqlSessionFactory build(InputStream inputStream) throws PropertyVetoException, DocumentException {
           //解析配置文件，封装到到Configuration
           Configuration configuration = new XMLConfigBuilder().parseConfig(inputStream);
           //创建sqlSessionFactory对象
           SqlSessionFactory sqlSessionFactory = new DefaultSqlSessionFactory(configuration);
           return sqlSessionFactory;
       }
   }

4. 通过sqlSessionFactory工厂创建SqlSession。

   /**
    * 默认SqlSessionFactory工厂
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   public class DefaultSqlSessionFactory implements SqlSessionFactory {
       private Configuration configuration;
   
       public DefaultSqlSessionFactory(Configuration configuration) {
           this.configuration = configuration;
       }
   
       @Override
       public SqlSession openSession() {
           return new DefaultSqlSession(this.configuration);
       }
   }

5. 通过SqlSession执行sql语句（此处包含动态代理的执行方法）。

   /**
    * 默认SqlSession
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   public class DefaultSqlSession implements SqlSession {
       private Configuration configuration;
   
       public DefaultSqlSession(Configuration configuration) {
           this.configuration = configuration;
       }
   
       @Override
       public  List selectList(String statementId, Object... params) throws Exception {
           Executor executor = new SimpleExecutor();
           MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
           List