原生JDBC

框架寫法

測試

原始碼地址

手寫Mybatis框架更有利於瞭解框架底層，做到知其然知其所以然。

原生JDBC

/**
 * 原生jdbc寫法
 *
 * @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, "張三");
            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寫法的弊端有：

1. 資料庫配置資訊及sql語句硬編碼。

2. 重複建立和關閉資料庫連線。

框架寫法

此處檔案的命名參考MyBatis原始碼命名風格，有利於後續檢視原始碼。

工程結構如下：

表結構如下：

框架大致流程如下：

1. 建立mapper.xml檔案用來儲存sql查詢語句，建立sqlMapConfig.xml來儲存資料庫配置資訊和mapper.xml檔案所在路徑。

   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. 按照面向物件程式設計思想，將第一步解析出來的內容分別封裝到MappedStatement和Configuration實體類中。

   /**
    * 配置檔案物件
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   @Data
   public class Configuration {
       private DataSource dataSource;
       //key:名稱空間+id
       private Map<String, MappedStatement> mappedStatementMap = new HashMap<>();
   }
   ​
   /**
    * mapper配置檔案物件
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   @Data
   public class MappedStatement {
       /**
        * 標識
        */
       private String id;
       /**
        * 返回結果型別
        */
       private String resultType;
       /**
        * 引數查詢型別
        */
       private String parameterType;
       /**
        * sql語句
        */
       private String sql;
   ​
   }
    
   

3. 通過SqlSessionFactoryBuilder構建者建立SqlSessionFactory。

   /**
    * SqlSessionFactory構建者
    *
    * @author lipangpang
    * @date 2022/3/13
    * @description
    */
   public class SqlSessionFactoryBuilder {
       /**
        * 構建
        *
        * @param inputStream 檔案配置流
        * @return
        * @throws PropertyVetoException
        * @throws DocumentException
        */
       public SqlSessionFactory build(InputStream inputStream) throws PropertyVetoException, DocumentException {
           //解析配置檔案，封裝到到Configuration
           Configuration configuration = new XMLConfigBuilder().parseConfig(inputStream);
           //建立sqlSessionFactory物件
           SqlSessionFactory sqlSessionFactory = new DefaultSqlSessionFactory(configuration);
           return sqlSessionFactory;
       }
   }

4. 通過sqlSessionFactory工廠建立SqlSession。

   /**
    * 預設SqlSessionFactory工廠
    *
    * @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. 通過SqlSession執行sql語句（此處包含動態代理的執行方法）。

   /**
    * 預設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("返回結果為空或返回結果過多");
           }
       }
   ​
       @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) {
           //通過jdk動態代理獲取物件
           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(這也是為什麼xml中id要和介面方法名一致)
                           String methodName = method.getName();
                           //類全路徑名(這也是為什麼xml中namespace要和介面全路徑一致)
                           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;
       }
   }

測試

測試程式碼：

/**
 * MyBatis測試類
 *
 * @author lipangpang
 * @date 2022/3/13
 * @description
 */
public class MybatisTest {
    public static void main(String[] args) throws Exception {
        //讀取配置檔案為流
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        //將配置檔案封裝成物件並建立SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        //建立SqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        MallUser user = new MallUser();
        user.setId(1L);
        user.setName("張三");
        MallUser userNew = new MallUser();
        userNew.setName("趙六");
        //查詢單個物件
        MallUser mallUserDb = sqlSession.selectOne("org.example.dao.IMallUserDao.selectOne", user);
        System.out.println("查詢單個物件:" + mallUserDb);
        //新增單個物件
        Integer insertSuccessNumber = sqlSession.insertOne("org.example.dao.IMallUserDao.insertOne", userNew);
        System.out.println("新增單個物件:" + insertSuccessNumber);
        //查詢所有物件
        List<MallUser> mallUsers = sqlSession.selectList("org.example.dao.IMallUserDao.queryAll");
        System.out.println("查詢所有物件:" + mallUsers);
        IMallUserDao mallUserDao = sqlSession.getMapper(IMallUserDao.class);
        //通過代理查詢所有物件
        List<MallUser> mallUsersByProxy = mallUserDao.queryAll();
        System.out.println("通過代理查詢所有物件:" + mallUsersByProxy);
    }
}

返回結果：

查詢單個物件:MallUser(id=1, name=張三)
新增單個物件:1
查詢所有物件:[MallUser(id=1, name=張三), MallUser(id=2, name=李四), MallUser(id=3, name=王五), MallUser(id=4, name=趙六)]
通過代理查詢所有物件:[MallUser(id=1, name=張三), MallUser(id=2, name=李四), MallUser(id=3, name=王五), MallUser(id=4, name=趙六)]

原始碼地址

https://gitee.com/lishihao_pm/demo-parent/tree/master/demo-mybatis