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:

手写MyBatis框架_第1张图片

表结构如下:

手写MyBatis框架_第2张图片

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
    
        
        
        
            insert into mall_user(name) values(#{name})
        
    
    
    MallRoleMapper.xml
    
        
        
        
            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 objects = executor.query(configuration, mappedStatement, params);
            return (List) objects;
        }
    
        @Override
        public  T selectOne(String statementId, Object... params) throws Exception {
            List 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 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 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 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...

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