笔记1：简易的持久层框架

思维逻辑：
在这里插入图片描述

前提为创建好的xml配置文件：sqlMapConfig.xml 以及IUserDao.java

<configuration>
    <dataSource>
        <property name="driverClass" value="com.mysql.jdbc.Driver"></property>
        <property name="jdbcUrl" value="jdbc:mysql:///lg"></property>
        <property name="username" value="root"></property>
        <property name="password" value="123456"></property>
    </dataSource>
	
	<!-- 指定Mapper路径，方便读取 --> 
    <mapper resource="UserMapper.xml"></mapper>
</configuration>

public interface IUserDao {
      
      

    List<User> findAll();

    User findByCondition(User user);

    void insert(User user);

    void update(User user);

    void deleteById(Integer id);
}

pom依赖：

	<dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.17</version>
    </dependency>
    <dependency>
        <groupId>c3p0</groupId>
        <artifactId>c3p0</artifactId>
        <version>0.9.1.2</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.12</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.10</version>
    </dependency>
    <dependency>
        <groupId>dom4j</groupId>
        <artifactId>dom4j</artifactId>
        <version>1.6.1</version>
    </dependency>
    <dependency>
        <groupId>jaxen</groupId>
        <artifactId>jaxen</artifactId>
        <version>1.1.6</version>
    </dependency>

开始编写简易的Mybatis, 首先创建SqlSessionFactoryBuilder.java 用于解析xml配置和jdbc操作

public class Resources {
      
      

    public static InputStream getResourceAsStream(String path) {
      
      
        InputStream resourceAsStream = Resources.class.getClassLoader().getResourceAsStream(path);
        return resourceAsStream;
    }
}

	public class SqlSessionFactoryBuilder {
      
      

    public SqlSessionFactory build(InputStream in) throws DocumentException, PropertyVetoException {
      
      
        XmlConfigBuilder xmlConfigBuilder = new XmlConfigBuilder();
        Configuration configuration = xmlConfigBuilder.parseConfig(in);

        return new DefaultSqlSessionFactory(configuration);
    }

}

XmlConfigBuilder.java解析xml配置，将解析出来的参数存入实体类Configuration.java及MappedStatement.java

	public class Configuration {
      
      

    private DataSource dataSource;

    /**
     * key: statementId -> namespace.id
     */
    Map<String, MappedStatement> mappedStatementMap = new HashMap<>(16);

    public DataSource getDataSource() {
      
      
        return dataSource;
    }

    public void setDataSource(DataSource dataSource) {
      
      
        this.dataSource = dataSource;
    }

    public Map<String, MappedStatement> getMappedStatementMap() {
      
      
        return mappedStatementMap;
    }

    public void setMappedStatementMap(Map<String, MappedStatement> mappedStatementMap) {
      
      
        this.mappedStatementMap = mappedStatementMap;
    }
}

public class MappedStatement {
      
      
    private String id;
    private String resultType;
    private String parameterType;
    private String sql;

    public String getId() {
      
      
        return id;
    }

    public void setId(String id) {
      
      
        this.id = id;
    }

    public String getResultType() {
      
      
        return resultType;
    }

    public void setResultType(String resultType) {
      
      
        this.resultType = resultType;
    }

    public String getParameterType() {
      
      
        return parameterType;
    }

    public void setParameterType(String parameterType) {
      
      
        this.parameterType = parameterType;
    }

    public String getSql() {
      
      
        return sql;
    }

    public void setSql(String sql) {
      
      
        this.sql = sql;
    }
}

public class XmlConfigBuilder {
      
      

    private final Configuration configuration;

    public XmlConfigBuilder() {
      
      
        this.configuration = new Configuration();
    }

    public Configuration parseConfig(InputStream in) throws DocumentException, PropertyVetoException {
      
      
        Document document = new SAXReader().read(in);
        Element rootElement = document.getRootElement();
        List<Element> list = rootElement.selectNodes("//property");
        Properties properties = new Properties();
        list.forEach(element -> {
      
      
            String name = element.attributeValue("name");
            String value = element.attributeValue("value");
            properties.setProperty(name, value);
        });

        ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();
        comboPooledDataSource.setDriverClass(properties.getProperty("driverClass"));
        comboPooledDataSource.setJdbcUrl(properties.getProperty("jdbcUrl"));
        comboPooledDataSource.setUser(properties.getProperty("username"));
        comboPooledDataSource.setPassword(properties.getProperty("password"));

        configuration.setDataSource(comboPooledDataSource);

        List<Element> mapperList = rootElement.selectNodes("//mapper");
        for (Element element : mapperList) {
      
      
            String mapperPath = element.attributeValue("resource");
            InputStream mapperIn = Resources.getResourceAsStream(mapperPath);
            XmlMapperBuilder xmlMapperBuilder = new XmlMapperBuilder(configuration);
            xmlMapperBuilder.parse(mapperIn);
        }

        return configuration;
    }
}

public class XmlMapperBuilder {
      
      

    private final Configuration configuration;

    public XmlMapperBuilder(Configuration configuration) {
      
      
        this.configuration = configuration;
    }

    public void parse(InputStream in) throws DocumentException {
      
      
        Document document = new SAXReader().read(in);
        Element rootElement = document.getRootElement();
        String namespace = rootElement.attributeValue("namespace");
        List<Element> list = new ArrayList<>();
        List<Element> selectList = rootElement.selectNodes("//select");
        List<Element> insertList = rootElement.selectNodes("//insert");
        List<Element> updateList = rootElement.selectNodes("//update");
        List<Element> deleteList = rootElement.selectNodes("//delete");
        if(selectList != null) {
      
      
            list.addAll(selectList);
        }
        if(insertList != null) {
      
      
            list.addAll(insertList);
        }
        if(updateList != null) {
      
      
            list.addAll(updateList);
        }
        if(deleteList != null) {
      
      
            list.addAll(deleteList);
        }
        list.forEach(element -> {
      
      
            String id = element.attributeValue("id");
            String resultType = element.attributeValue("resultType");
            String parameterType = element.attributeValue("parameterType");
            String sql = element.getTextTrim();
            MappedStatement mappedStatement = new MappedStatement();
            mappedStatement.setId(id);
            mappedStatement.setParameterType(parameterType);
            mappedStatement.setResultType(resultType);
            mappedStatement.setSql(sql);
            configuration.getMappedStatementMap().put(namespace+"."+id, mappedStatement);
        });
    }
}

解析好xml配置后，将参数传递并构造sql

public interface SqlSessionFactory {
      
      

    public SqlSession openSession();
}

public class DefaultSqlSessionFactory implements SqlSessionFactory {
      
      

    private final Configuration configuration;

    public DefaultSqlSessionFactory(Configuration configuration) {
      
      
        this.configuration = configuration;
    }


    @Override
    public SqlSession openSession() {
      
      
        return new DefaultSqlSession(configuration);
    }

	public interface SqlSession {
      
      

    <E> List<E> selectList(String statementId, Object... params) throws Exception;

    <T> T selectOne(String statementId, Object... params) throws Exception;

    <T> T getMapper(Class<?> mapperClass);

    Object insert(String statementId, Object... params) throws Exception;

    Object update(String statementId, Object... params) throws Exception;

    Object delete(String statementId, Object... params) throws Exception;
}

然后在DefaultSqlSession里进行jdbc方法的实现,这里的getMapper为动态代理，用于IUserDao.java的调用

public class DefaultSqlSession implements SqlSession {
      
      

    private final Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
      
      
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {
      
      
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> queryList = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) queryList;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
      
      
        List<Object> objects = selectList(statementId, params);
        if(objects == null || objects.size() > 1) {
      
      
            throw new RuntimeException("结果为空或结果过多");
        } else {
      
      
            return (T) objects.get(0);
        }
    }

    @Override
    public Object insert(String statementId, Object... params) throws Exception {
      
      
        return update(statementId, params);
    }

    @Override
    public Object update(String statementId, Object... params) throws Exception {
      
      
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public Object delete(String statementId, Object... params) throws Exception {
      
      
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.delete(configuration, mappedStatement, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
      
      
        //使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{
      
      mapperClass}, new InvocationHandler() {
      
      
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      
      
                // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
                // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                // 方法名：findAll
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();

                String statementId = className + "." + methodName;

                // 准备参数2：params:args
                // 获取被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();
                MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                String sql = mappedStatement.getSql();
                if (genericReturnType instanceof ParameterizedType) {
      
      
                    return selectList(statementId, args);
                } else if(sql.startsWith("update")) {
      
      
                    return update(statementId, args);
                } else if(sql.startsWith("insert")) {
      
      
                    return insert(statementId, args);
                } else if(sql.startsWith("delete")) {
      
      
                    return delete(statementId, args);
                } else {
      
      
                    return selectOne(statementId, args);
                }
            }
        });
        return (T) proxyInstance;
    }
}

对应数据库操作的实现

public interface Executor {
      
      
    <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception;

    Integer update(Configuration configuration, MappedStatement mappedStatement, Object[] params) throws Exception;

    Integer delete(Configuration configuration, MappedStatement mappedStatement, Object[] params) throws Exception;
}

public class BoundSql {
      
      
    private String sqlText;
    private List<ParameterMapping> parameterMappings = new ArrayList<>();

    public BoundSql(String sqlText, List<ParameterMapping> parameterMappings) {
      
      
        this.sqlText = sqlText;
        this.parameterMappings = parameterMappings;
    }

    public String getSqlText() {
      
      
        return sqlText;
    }

    public void setSqlText(String sqlText) {
      
      
        this.sqlText = sqlText;
    }

    public List<ParameterMapping> getParameterMappings() {
      
      
        return parameterMappings;
    }

    public void setParameterMappings(List<ParameterMapping> parameterMappings) {
      
      
        this.parameterMappings = parameterMappings;
    }
}

public class SimpleExecutor implements Executor {
      
      
    @Override
    public <E> List<E> query(Configuration configuration, MappedStatement mappedStatement, Object... params) throws Exception {
      
      
        //创建链接
        Connection connection = configuration.getDataSource().getConnection();

        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        //设置参数
        String parameterType = mappedStatement.getParameterType();
        Class<?> parameterTypeClass = getClassType(parameterType);
        if(parameterTypeClass != null) {
      
      
            List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
            for (int i = 0; i < parameterMappings.size(); i++) {
      
      
                ParameterMapping parameterMapping = parameterMappings.get(i);
                String content = parameterMapping.getContent();

                Field declaredField = parameterTypeClass.getDeclaredField(content);
                declaredField.setAccessible(true);
                Object o = declaredField.get(params[0]);

                preparedStatement.setObject(i + 1, o);
            }
        }

        //执行
        ResultSet resultSet = preparedStatement.executeQuery();

        //封装返回结果
        List<Object> resultList = new ArrayList<>();
        String resultType = mappedStatement.getResultType();
        Class<?> resultTypeClass = getClassType(resultType);
        Object o;
        ResultSetMetaData metaData = resultSet.getMetaData();
        if(resultTypeClass != null) {
      
      
            while (resultSet.next()) {
      
      
                o = resultTypeClass.newInstance();
                for (int i = 1; i < metaData.getColumnCount(); i++) {
      
      
                    String columnName = metaData.getColumnName(i);
                    PropertyDescriptor propertyDescriptor = new PropertyDescriptor(columnName, resultTypeClass);
                    Method writeMethod = propertyDescriptor.getWriteMethod();
                    Object value = resultSet.getObject(columnName);
                    writeMethod.invoke(o, value);
                }
                resultList.add(o);
            }
        }

        return (List<E>) resultList;
    }

    @Override
    public Integer update(Configuration configuration, MappedStatement mappedStatement, Object[] params) throws Exception {
      
      
        //创建链接
        Connection connection = configuration.getDataSource().getConnection();

        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        //设置参数
        String parameterType = mappedStatement.getParameterType();
        Class<?> parameterTypeClass = getClassType(parameterType);
        if(parameterTypeClass != null) {
      
      
            List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
            ParameterMapping parameterMapping;
            for (int i = 0; i < parameterMappings.size(); i++) {
      
      
                parameterMapping = parameterMappings.get(i);
                String content = parameterMapping.getContent();

                Field declaredField = parameterTypeClass.getDeclaredField(content);
                declaredField.setAccessible(true);
                Object value = declaredField.get(params[0]);

                preparedStatement.setObject(i + 1, value);
            }

            return preparedStatement.executeUpdate();

        } else {
      
      
            throw new RuntimeException(mappedStatement.getId() + ": parameterType未定义");
        }
    }

    @Override
    public Integer delete(Configuration configuration, MappedStatement mappedStatement, Object[] params) throws Exception {
      
      
        //创建链接
        Connection connection = configuration.getDataSource().getConnection();

        String sql = mappedStatement.getSql();
        BoundSql boundSql = getBoundSql(sql);

        PreparedStatement preparedStatement = connection.prepareStatement(boundSql.getSqlText());

        preparedStatement.setObject(1, params[0]);

        return preparedStatement.executeUpdate();
    }

    private Class<?> getClassType(String parameterType) throws ClassNotFoundException {
      
      
        if(!StringUtils.isNullOrEmpty(parameterType)) {
      
      
            return Class.forName(parameterType);
        }

        return null;
    }

    private BoundSql getBoundSql(String sql) {
      
      
        ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler();
        GenericTokenParser genericTokenParser = new GenericTokenParser("#{", "}", handler);
        String sqlOut = genericTokenParser.parse(sql);
        List<ParameterMapping> parameterMappings = handler.getParameterMappings();

        return new BoundSql(sqlOut, parameterMappings);
    }
}

其中GenericTokenParser为Mybatis的源码里的方法。

测试用例

public class IPersistenceTest {
      
      

    @Test
    public void test() throws Exception {
      
      
        InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        User user = new User();
        user.setId(3);
        user.setUsername("Jack Ma");
        user.setPassword("123");
        user.setBirthday("2020-12-11");
        IUserDao userDao = sqlSession.getMapper(IUserDao.class);

        //insert
        userDao.insert(user);

        //update
        user.setPassword("1234");
        userDao.update(user);

        //delete
        userDao.deleteById(3);
    }
}

P.S. GenericTokenParser工具：
链接：https://pan.baidu.com/s/1Drec7juYHD1-Uka-v5vQWw
提取码：oukl

笔记1：简易的持久层框架

笔记1：简易的持久层框架

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