1. 首先了解一下mybatis，包含核心jar ，以及spring相关jar.
<!-- Mybatis相关组件 --> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.3.0</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> <version>1.2.3</version> </dependency>
- 系列的文章也是mybatis 3.3.0和mybatis-spring1.2.3分析
- mybatis jar包中只要包含mybaits的核心业务sqlsession,sqlsessionFactory,configuration
- mybatis-spring 包中只要是和spring的相关集成，sqlSessionFactoryBean、transaction
2. 加载mybatis
本文以spring中加载mybatis为参考，由一下代码加载mybatis
<!-- 配置集成Mybatis --> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="dataSource" /> <property name="configLocation" value="classpath:/config/SQLMapConfig.xml" /> <property name="mapperLocations" value="classpath*:com/chihiro/*/**/infra/mybatis/*Mapper.xml" /> </bean>
- sqlSessionFactory接口（mybatis包核心接口）
a、接口中有如下方法。子类中含有所有方法的实现
public interface SqlSessionFactory { SqlSession openSession(); SqlSession openSession(boolean autoCommit); SqlSession openSession(Connection connection); SqlSession openSession(TransactionIsolationLevel level); SqlSession openSession(ExecutorType execType); SqlSession openSession(ExecutorType execType, boolean autoCommit); SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level); SqlSession openSession(ExecutorType execType, Connection connection); Configuration getConfiguration(); }
b、接口的实现类，由sqlSessionFactoryBean产生的是默认的SqlSessionFactory(DefaultSqlSessionFactory)
- sqlSessionFactoryBean(mybatis-spring包下面的创建工厂的Bean，由spring 加载初始化)
a、从上述mybais的加载，可以看到，构造sqlSessionFactoryBean之后给了默认的属性值，dataSource，configLocation，mapper
public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> { private static final Log LOGGER = LogFactory.getLog(SqlSessionFactoryBean.class); private Resource configLocation; private Resource[] mapperLocations; private DataSource dataSource; //SqlSessionFactory 构造的协助类 private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); private SqlSessionFactory sqlSessionFactory; //创建sqlSessionFactory的方法体 protected SqlSessionFactory buildSqlSessionFactory() throws IOException { Configuration configuration; XMLConfigBuilder xmlConfigBuilder = null; if (this.configLocation != null) { xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration(); } else { if (LOGGER.isDebugEnabled()) { LOGGER.debug("Property 'configLocation' not specified, using default MyBatis Configuration"); } configuration = new Configuration(); configuration.setVariables(this.configurationProperties); } ... return this.sqlSessionFactoryBuilder.build(configuration); }ss @Override public void afterPropertiesSet() throws Exception { notNull(dataSource, "Property 'dataSource' is required"); notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required"); //调用方法创建sqlSessionFactory this.sqlSessionFactory = buildSqlSessionFactory(); } @Override public void onApplicationEvent(ApplicationEvent event) { if (failFast && event instanceof ContextRefreshedEvent) { // fail-fast -> check all statements are completed this.sqlSessionFactory.getConfiguration().getMappedStatementNames(); } } }
- 实现3个相关接口的作用
FactoryBean接口：实现了该接口的类，在调用getBean（获取bean对象）的时候会返回该工厂返回的实例对象，也就是再调一次getObject方法返回工厂的实例。
InitializingBean接口：实现了这个接口，那么当bean初始化的时候，spring就会调用该接口的实现类的afterPropertiesSet方法，去实现当spring初始化该Bean的时候所需要的逻辑。
ApplicationListener接口：实现了该接口，如果注册了该监听的话，那么就可以了监听到Spring的一些事件，然后做相应的处理
2.在bean初始化之后，可以看见，回调方法afterPropertiesSet，在里面构造configuration对象。以及产生sqlSession
Configuration类：可以发现配置中读取configuration。（核心配置，关联mybatis整个生命周期）
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration();
3.由sqlSessionFactoryBuild 构造sqlSessionFactory
public class SqlSessionFactoryBuilder { public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config); } }
4. 建设者模式
生产sqlSessionFacoty 使用了建设者模式（Builder）。其构造过程主要注入了Configuration的实例对象，sqlSessionFactoryBuilder 扮演具体的建造者，configuration类主要负责建造细节的工作，sqlSessionFactory则是建造出来的产品
- 总结
