在《spring中FactoryBean是什么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，
/**
* 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，返回其对象
if (object == null) {
// Return bean instance from factory.
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}