一次性讲清楚spring中bean的生命周期之二：FactoryBean的前世今生

Bertha 。 2023-10-03 09:56 19阅读 0赞

## 前言 ##

在《[spring中FactoryBean是什么bean][spring_FactoryBean_bean]》一文中，带着小伙伴学习了spring中的FactoryBean，了解了到了FactoryBean其实是一种生产Bean的bean，也就是FactroyBean的前世是Bean，今生还是Bean，小伙伴要疑惑了都是Bean，但是此Bean非彼Bean。今天带着小伙伴从源码的角度来分析下FactoryBean，重点是getObjectForBeanInstance方法的分析。

## 前世 ##

在前面说到FactoryBean的前世是一个Bean，是指是一个FactoryBean的实例。先来看下getObjectForBeanInstance方法，

![复制代码][48304ba5e6f9fe08f3fa1abda7d326ab.png]

/**
         * Get the object for the given bean instance, either the bean
         * instance itself or its created object in case of a FactoryBean.
         */
        protected Object getObjectForBeanInstance(
                Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
    
            // Don't let calling code try to dereference the factory if the bean isn't a factory.
            //1、判断name是否以&开头
            if (BeanFactoryUtils.isFactoryDereference(name)) {
                if (beanInstance instanceof NullBean) {
                    return beanInstance;
                }
                if (!(beanInstance instanceof FactoryBean)) {
                    throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
                }
            }
    
            // 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.
             //beanInstance不是FactoryBean的实例或name以&开头
            if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
                return beanInstance;
            }
    
            Object object = null;
            //mbd即beanDefinition为空，从缓存中取
            if (mbd == null) {
                object = getCachedObjectForFactoryBean(beanName);
            }
            //缓存中没有，则调用FactoryBean的getObject方法

[spring_FactoryBean_bean]: https://www.cnblogs.com/teach/p/14951920.html
[48304ba5e6f9fe08f3fa1abda7d326ab.png]: https://img-blog.csdnimg.cn/img_convert/48304ba5e6f9fe08f3fa1abda7d326ab.png