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
   <configuration>
       <dataSource>
           <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
           <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=Asia/Shanghai"></property>
           <property name="username" value="root"></property>
           <property name="password" value="123456"></property>
       </dataSource>
   
       <mapper resource="MallUserMapper.xml"></mapper>
       <mapper resource="MallRoleMapper.xml"></mapper>
   </configuration>
   
   MallUserMapper.xml
   <mapper namespace="org.example.dao.IMallUserDao">
       <select id="queryAll" parameterType="org.example.entity.MallUser" resultType="org.example.entity.MallUser">
           select * from mall_user
       </select>
       <select id="selectOne" parameterType="org.example.entity.MallUser" resultType="org.example.entity.MallUser">
           select * from mall_user where id = #{id} and name = #{name}
       </select>
       <insert id="insertOne" parameterType="org.example.entity.MallUser" resultType="int">
           insert into mall_user(name) values(#{name})
       </insert>
   </mapper>
   
   MallRoleMapper.xml
   <mapper namespace="org.example.dao.IMallRoleDao">
       <select id="queryAll" parameterType="org.example.entity.MallRole" resultType="org.example.entity.MallRole">
           select * from mall_role
       </select>
       <select id="selectOne" parameterType="org.example.entity.MallRole" resultType="org.example.entity.MallRole">
           select * from mall_role where id = #{id} and name = #{name}
       </select>
       <insert id="insertOne" parameterType="org.example.entity.MallRole" resultType="int">
           insert into mall_role(name) values(#{name})
       </insert>
   </mapper>

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<String, MappedStatement> 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 <E> List<E> selectList(String statementId, Object... params) throws Exception {
           Executor executor = new SimpleExecutor();
           MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
           List<Object> objects = executor.query(configuration, mappedStatement, params);
           return (List<E>) objects;
       }
   
       @Override
       public <T> T selectOne(String statementId, Object... params) throws Exception {
           List<Object> objects = this.selectList(statementId, params);
           if (objects != null && objects.size() == 1) {
               return (T) objects.get(0);
           } else {
               throw new RuntimeException("返回结果为空或返回结果过多");
           }
       }
   
       @Override
       public Integer insertOne(String statementId, Object... params) throws Exception {
           Executor executor = new SimpleExecutor();
           MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
           return executor.save(configuration, mappedStatement, params);
       }
   
       @Override
       public <T> T getMapper(Class<?> mapperClass) {
           //通过jdk动态代理获取对象
           Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new
                   InvocationHandler() {
                       @Override
                       public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                           //方法名(这也是为什么xml中id要和接口方法名一致)
                           String methodName = method.getName();
                           //类全路径名(这也是为什么xml中namespace要和接口全路径一致)
                           String className = method.getDeclaringClass().getName();
                           String statementId = className + "." + methodName;
                           Type genericReturnType = method.getGenericReturnType();
                           if (genericReturnType instanceof ParameterizedType) {
                               return selectList(statementId, args);
                           }
                           if (genericReturnType.getTypeName().contains("Integer")) {
                               return insertOne(statementId, args);
                           }
                           return selectOne(statementId, args);
                       }
                   });
           return (T) proxyInstance;
       }
   }

测试

测试代码：

/**
 * MyBatis测试类
 *
 * @author lipangpang
 * @date 2022/3/13
 * @description
 */
public class MybatisTest {
    public static void main(String[] args) throws Exception {
        //读取配置文件为流
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        //将配置文件封装成对象并创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //创建SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        MallUser user = new MallUser();
        user.setId(1L);
        user.setName("张三");
        MallUser userNew = new MallUser();
        userNew.setName("赵六");
        //查询单个对象
        MallUser mallUserDb = sqlSession.selectOne("org.example.dao.IMallUserDao.selectOne", user);
        System.out.println("查询单个对象:" + mallUserDb);
        //新增单个对象
        Integer insertSuccessNumber = sqlSession.insertOne("org.example.dao.IMallUserDao.insertOne", userNew);
        System.out.println("新增单个对象:" + insertSuccessNumber);
        //查询所有对象
        List<MallUser> mallUsers = sqlSession.selectList("org.example.dao.IMallUserDao.queryAll");
        System.out.println("查询所有对象:" + mallUsers);
        IMallUserDao mallUserDao = sqlSession.getMapper(IMallUserDao.class);
        //通过代理查询所有对象
        List<MallUser> mallUsersByProxy = mallUserDao.queryAll();
        System.out.println("通过代理查询所有对象:" + mallUsersByProxy);
    }
}

返回结果：

查询单个对象:MallUser(id=1, name=张三)
新增单个对象:1
查询所有对象:[MallUser(id=1, name=张三), MallUser(id=2, name=李四), MallUser(id=3, name=王五), MallUser(id=4, name=赵六)]
通过代理查询所有对象:[MallUser(id=1, name=张三), MallUser(id=2, name=李四), MallUser(id=3, name=王五), MallUser(id=4, name=赵六)]

源码地址

https://gitee.com/lishihao_pm...