mybatis源碼分析（1）-----sqlSessionFactory創建

1. 首先了解一下mybatis，包含核心jar ，以及spring相關jar.

<!-- Mybatis相關組件 -->
<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的核心業務sqlsession,sqlsessionFactory,configuration
• mybatis-spring 包中只要是和spring的相關集成，sqlSessionFactoryBean、transaction

 

2. 加載mybatis

本文以spring中加載mybatis為參考，由一下代碼加載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。子類中含有所有方法的實現

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、接口的實現類，由sqlSessionFactoryBean產生的是默認的SqlSessionFactory(DefaultSqlSessionFactory)

　　

 

•  sqlSessionFactoryBean(mybatis-spring包下面的創建工廠的Bean，由spring 加載初始化)

　　a、從上述mybais的加載，可以看到，構造sqlSessionFactoryBean之后給了默認的屬性值，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 構造的協助類
  private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();

  private SqlSessionFactory sqlSessionFactory;

  //創建sqlSessionFactory的方法體
  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");
    //調用方法創建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();
    }
  }

}

 

1. 實現3個相關接口的作用

　　　　FactoryBean接口：實現了該接口的類，在調用getBean（獲取bean對象）的時候會返回該工廠返回的實例對象，也就是再調一次getObject方法返回工廠的實例。

　　　　InitializingBean接口：實現了這個接口，那么當bean初始化的時候，spring就會調用該接口的實現類的afterPropertiesSet方法，去實現當spring初始化該Bean的時候所需要的邏輯。

　　　　ApplicationListener接口：實現了該接口，如果注冊了該監聽的話，那么就可以了監聽到Spring的一些事件，然后做相應的處理

     2.在bean初始化之后，可以看見，回調方法afterPropertiesSet，在里面構造configuration對象。以及產生sqlSession

　　　　Configuration類：可以發現配置中讀取configuration。（核心配置，關聯mybatis整個生命周期）

      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      configuration = xmlConfigBuilder.getConfiguration();

    3.由sqlSessionFactoryBuild 構造sqlSessionFactory

public class SqlSessionFactoryBuilder {
    
  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

}

 

4. 建設者模式

　　生產sqlSessionFacoty 使用了建設者模式（Builder）。其構造過程主要注入了Configuration的實例對象，sqlSessionFactoryBuilder 扮演具體的建造者，configuration類主要負責建造細節的工作，sqlSessionFactory則是建造出來的產品

 

 

• 　　總結