mybatis源码分析（1）-----sqlSessionFactory创建

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