使用过SSM的框架的都知道mybatis这个持久层框架，今天小编就来简单说说这个框架的核心工厂类sqlSessionFactory的加载过程，一般的SSM框架我们都会在spring的application.xml中引入如下的配置：

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        <property name="configLocation" value="classpath:config/mybatis-config.xml"></property>
    </bean>

其中的SqlSessionFactoryBean便是加载sqlSessionFactory的入口，首先我们来看看这个类的源代码：

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;

 private TransactionFactory transactionFactory;

  private Properties configurationProperties;

  private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();

  private SqlSessionFactory sqlSessionFactory;

其中标红的两处，就是我们在application.xml中注入的两个属性，从源码中我们可以看出该类实现了InitializingBean接口，实现了其afterPropertiesSet（）方法，

该方法是在当前bean的所有属性被初始化完成之后再执行，也就是其中的datasource和configurationProperties等属性，接下来我们看看这个方法主要干什么了？

public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");

    this.sqlSessionFactory = buildSqlSessionFactory();
  }

其中第5行很明显的buildSqlSessionFactory（）方法初始化了sqlSessionFactory ，接下来我们看看这个方法的主要行为：

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);
    }

    if (this.objectFactory != null) {
      configuration.setObjectFactory(this.objectFactory);
    }

    if (this.objectWrapperFactory != null) {
      configuration.setObjectWrapperFactory(this.objectWrapperFactory);
    }