通过前面的章节我们知道Bean的创建在doCreateBean中是怎么完成的。
首先，通过createBeanInstance对Bean进行实例化
然后，通过populateBean方法完成依赖注入
而BeanPostProcessor也就是Bean的后置处理，是在完成依赖注入后，通过initializeBean方法调用进行的。
后置：指的是在Bean实例化后，BeanPostProcessor都是在createBeanInstance对Bean进行实例化后执行的
try {
this.populateBean(beanName, mbd, instanceWrapper);
exposedObject = this.initializeBean(beanName, exposedObject, mbd);
} catch (Throwable var18) {
if (var18 instanceof BeanCreationException && beanName.equals(((BeanCreationException)var18).getBeanName())) {
throw (BeanCreationException)var18;
}
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", var18);
}
initializeBean方法中
调用了applyBeanPostProcessorsBeforeInitialization处理Bean初始化前的处理
调用了invokeInitMethods执行初始化方法
调用了applyBeanPostProcessorsAfterInitialization处理Bean初始化后的处理
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(() -> {
this.invokeAwareMethods(beanName, bean);
return null;
}, this.getAccessControlContext());
} else {
this.invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = this.applyBeanPostProcessorsBeforeInitialization(bean, beanName);
}
try {
this.invokeInitMethods(beanName, wrappedBean, mbd);
} catch (Throwable var6) {
throw new BeanCreationException(mbd != null ? mbd.getResourceDescription() : null, beanName, "Invocation of init method failed", var6);
}
if (mbd == null || !mbd.isSynthetic()) {
wrappedBean = this.applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}
applyBeanPostProcessorsBeforeInitialization方法中，调用了BeanPostProcessor的postProcessBeforeInitialization方法，该方法在Bean的初始化前执行
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
Object result = existingBean;
Object current;
for(Iterator var4 = this.getBeanPostProcessors().iterator(); var4.hasNext(); result = current) {
BeanPostProcessor processor = (BeanPostProcessor)var4.next();
current = processor.postProcessBeforeInitialization(result, beanName);
if (current == null) {
return result;
}
}
return result;
}
applyBeanPostProcessorsAfterInitialization方法中，调用了BeanPostProcessor的postProcessAfterInitialization方法，该方法在Bean的初始化后执行
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName) throws BeansException {
Object result = existingBean;
Object current;
for(Iterator var4 = this.getBeanPostProcessors().iterator(); var4.hasNext(); result = current) {
BeanPostProcessor processor = (BeanPostProcessor)var4.next();
current = processor.postProcessAfterInitialization(result, beanName);
if (current == null) {
return result;
}
}
return result;
}