spring对于BeanFactory取得对象

今天在看spring与hibernate的代码，发现了一个地方非常难理解，就是我以前搭建的一个spring+hibernate的代码中在DAO中注入HibernateDaoSupport中注入的是的spring的LocalSessionFactoryBean,而属性确实hibernate的SessionFactory，考虑不通，按照正常的思路应该是要保ClassCaseException的，于是查询了一下spring refreence，发现了一句话的描述：
“This may be done by prepending the bean id with & when calling the getBean method of BeanFactory(including ApplicationContext). So for a given FactoryBean with an id myBean, invoking getBean("myBean")on the BeanFactory will return the product of the FactoryBean, but invoking getBean("&myBean") will returnthe FactoryBean instance itself”

这句话表明了事情的原委，如果是factorybean的话，他会取得他的方法的产品，所以诸如的是HibernateDaoSupport的产品，就是getSessionFactory的返回值。一个细小的地方，造成误会。
spring处理此处的地方代码如下，可以解释spring如何进行的数据处理

//仔细察看spring的注释
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
  // If it's a FactoryBean, we use it to create a bean instance, unless the
  // caller actually wants a reference to the factory.
  if (beanInstance instanceof FactoryBean) {
   if (!isFactoryDereference(name)) {
    // Return bean instance from factory.
    FactoryBean factory = (FactoryBean) beanInstance;
    if (logger.isDebugEnabled()) {
     logger.debug("Bean with name '" + beanName + "' is a factory bean");
    }
    try {
     beanInstance = factory.getObject();
    }
    catch (Exception ex) {
     throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
    }
    if (beanInstance == null) {
     throw new FactoryBeanNotInitializedException(
         beanName, "FactoryBean returned null object: " +
       "probably not fully initialized (maybe due to circular bean reference)");
    }
   }
   else {
     // The user wants the factory itself.
    if (logger.isDebugEnabled()) {
     logger.debug("Calling code asked for FactoryBean instance for name '" + beanName + "'");
    }
   }
  }

 

评论

1 楼 dwangel 2008-02-23  

如果该 id所引用的bean是FactoryBean实例，则检查是否使用了&，
如果没有则调用FactoryBean的getObject方法来取得产品。