spring 强大的钩子函数总结

Spring是我们经常使用的一个框架，它功能之一是提供了我们管理bean对象的手段，而且它提供了很多钩子方法给我们使用。什么是钩子方法呢？钩子方法就是：在bean的生命周期之中，经历了一系列的过程之中，Spring留给我们的一个后门，让我们能在Spring的生命周期之中执行我们想要的方法，从而实现我们想要的功能。接下来我们介绍一下生命周期，然后一个一个介绍我见过的样例或者我自己写的样例。

Spring生命周期的各种Aware

Spring的生命周期（我们撇开网络上很多资料，因为我觉得网络上很多资料要么不全，要么分不清context和beanFactory，然后将context的一些过程归入beanFactory之中。我这里只看Spring官方文档，我看的是5.3.0-SNAPSHOT版本的。）

上面列表说的114个初始化方法，13个销毁方法。这就是我说的钩子方法，只要你进程并实现了对应的方法，spring就会帮我们调用这些方法。

然后针对上面的bean lifecycle 我这里用一个简单的例子给大家演示一下：

<span style="color:#000000"><code class="language-java"><span style="color:#6679cc">public</span> <span style="color:#6679cc">class</span> BeanLifecycle <span style="color:#6679cc">implements</span> BeanNameAware<span style="color:#999999">,</span> BeanClassLoaderAware<span style="color:#999999">,</span> BeanFactoryAware<span style="color:#999999">,</span> EnvironmentAware<span style="color:#999999">,</span>EmbeddedValueResolverAware<span style="color:#999999">,</span> ResourceLoaderAware<span style="color:#999999">,</span> ApplicationEventPublisherAware<span style="color:#999999">,</span> MessageSourceAware<span style="color:#999999">,</span>ApplicationContextAware<span style="color:#999999">,</span> ServletContextAware<span style="color:#999999">,</span> BeanPostProcessor<span style="color:#999999">,</span> InitializingBean<span style="color:#999999">,</span> DestructionAwareBeanPostProcessor<span style="color:#999999">,</span>DisposableBean<span style="color:#999999">{</span><span style="color:#6b7394">/*** BeanNameAware 的 setBeanName，这个是第一个触发*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setBeanName</span><span style="color:#999999">(</span>String s<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第一个执行 bean name = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** BeanClassLoaderAware 的 setBeanClassLoader*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setBeanClassLoader</span><span style="color:#999999">(</span>ClassLoader classLoader<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第二个执行  classLoader = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** BeanFactoryAware 的 setBeanFactory*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setBeanFactory</span><span style="color:#999999">(</span>BeanFactory beanFactory<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第三个执行 beanFactory = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** EnvironmentAware 的 setEnvironment*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setEnvironment</span><span style="color:#999999">(</span>Environment environment<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第四个执行 environment = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** EmbeddedValueResolverAware 的 EmbeddedValueResolverAware*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setEmbeddedValueResolver</span><span style="color:#999999">(</span>StringValueResolver resolver<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第五个执行 resolver = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** ResourceLoaderAware 的 setResourceLoader*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setResourceLoader</span><span style="color:#999999">(</span>ResourceLoader resourceLoader<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第六个执行 resourceLoader = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** ApplicationEventPublisherAware 的 setApplicationEventPublisher*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setApplicationEventPublisher</span><span style="color:#999999">(</span>ApplicationEventPublisher applicationEventPublisher<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第七个执行 applicationEventPublisher = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** MessageSourceAware 的 setMessageSource*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setMessageSource</span><span style="color:#999999">(</span>MessageSource messageSource<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第八个执行 messageSource = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** ApplicationContextAware 的 setApplicationContext*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setApplicationContext</span><span style="color:#999999">(</span>ApplicationContext applicationContext<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第九个执行 applicationContext = "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** ServletContextAware 的 setServletContext*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setServletContext</span><span style="color:#999999">(</span>ServletContext servletContext<span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十个执行 servletContext = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** BeanPostProcessor 的 postProcessBeforeInitialization*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> Object <span style="color:#3d8fd1">postProcessBeforeInitialization</span><span style="color:#999999">(</span>Object bean<span style="color:#999999">,</span> String beanName<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十一个执行 postProcessBeforeInitialization bean = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十一个执行 postProcessBeforeInitialization beanName = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6679cc">return</span> bean<span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** InitializingBean 的 afterPropertiesSet*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">afterPropertiesSet</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> Exception <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十二个执行 = afterPropertiesSet"</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** 指定 的 initMethod*/</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">initMethod</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十三个执行 = initMethod"</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** BeanPostProcessor 的 postProcessAfterInitialization*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> Object <span style="color:#3d8fd1">postProcessAfterInitialization</span><span style="color:#999999">(</span>Object bean<span style="color:#999999">,</span> String beanName<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十四个执行 postProcessAfterInitialization bean = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第十四个执行 postProcessAfterInitialization beanName = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6679cc">return</span> bean<span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** DestructionAwareBeanPostProcessor 的 postProcessBeforeDestruction*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">postProcessBeforeDestruction</span><span style="color:#999999">(</span>Object o<span style="color:#999999">,</span> String s<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第一个执行的销毁方法 o = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第一个执行的销毁方法 s = "</span> <span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6b7394">/*** DisposableBean 的 destroy*/</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">destroy</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> Exception <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第二个执行的销毁方法 = destroy"</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">destroyMethod</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#999999">{</span>System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#3d8fd1">println</span><span style="color:#999999">(</span><span style="color:#ac9739">"第三个执行的销毁方法 "</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span>

然后我创建了下面一个测试用例：

<span style="color:#000000"><code class="language-java"><span style="color:#999999">@SpringBootApplication</span>
<span style="color:#6679cc">public</span> <span style="color:#6679cc">class</span> LifecycleMain <span style="color:#999999">{</span><span style="color:#999999">@Bean</span><span style="color:#999999">(</span>initMethod <span style="color:#ac9739">=</span> <span style="color:#ac9739">"initMethod"</span><span style="color:#999999">,</span> destroyMethod <span style="color:#ac9739">=</span> <span style="color:#ac9739">"destroyMethod"</span><span style="color:#999999">)</span><span style="color:#6679cc">public</span> BeanLifecycle <span style="color:#3d8fd1">beanLifecycle</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#999999">{</span><span style="color:#6679cc">return</span> <span style="color:#6679cc">new</span> BeanLifecycle<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#999999">@Bean</span><span style="color:#999999">(</span>initMethod <span style="color:#ac9739">=</span> <span style="color:#ac9739">"initMethod"</span><span style="color:#999999">,</span> destroyMethod <span style="color:#ac9739">=</span> <span style="color:#ac9739">"destroyMethod"</span><span style="color:#999999">)</span><span style="color:#6679cc">public</span> BeanLifecycle <span style="color:#3d8fd1">beanLifecycle2</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#999999">{</span><span style="color:#6679cc">return</span> <span style="color:#6679cc">new</span> BeanLifecycle<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">static</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">main</span><span style="color:#999999">(</span>String<span style="color:#999999">[</span><span style="color:#999999">]</span> args<span style="color:#999999">)</span> <span style="color:#999999">{</span>ConfigurableApplicationContext context <span style="color:#ac9739">=</span> <span style="color:#6679cc">new</span> SpringApplication<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#3d8fd1">run</span><span style="color:#999999">(</span>LifecycleMain<span style="color:#999999">.</span><span style="color:#6679cc">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>context<span style="color:#999999">.</span><span style="color:#3d8fd1">close</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>  <span style="color:#6b7394">//这个方法用来触发destroy-method</span><span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span>

output如下：

<span style="color:#000000"><code>第一个执行 bean name =
第二个执行  classLoader =
第三个执行 beanFactory =
第四个执行 environment =
第五个执行 resolver =
第六个执行 resourceLoader =
第七个执行 applicationEventPublisher =
第八个执行 messageSource =
第九个执行 applicationContext =
第十二个执行 = afterPropertiesSet
第十三个执行 = initMethod
第一个执行 bean name =
第二个执行  classLoader =
第三个执行 beanFactory =
第四个执行 environment =
第五个执行 resolver =
第六个执行 resourceLoader =
第七个执行 applicationEventPublisher =
第八个执行 messageSource =
第九个执行 applicationContext =
第十二个执行 = afterPropertiesSet
第十三个执行 = initMethod
第十一个执行 bean =
第十一个执行 beanName =
第十一个执行 bean =
第十一个执行 beanName =
第十四个执行 bean =
第十四个执行 beanName =
第十四个执行 bean =
第十四个执行 beanName =
第二个执行的销毁方法 = destroy
第三个执行的销毁方法
第二个执行的销毁方法 = destroy
第三个执行的销毁方法
</code></span>

这里我把后面输出的对象都去掉了，因为输出结果太长影响我们观看。

然后我先简单说说Aware，Aware英文翻译是知道的意思，Aware接口作用就是其实就是你想知道什么信息，然后就实现什么样的Aware，Spring会通过setXXX方法，将你想要知道的信息通过参数传递给你。

所以 BeanNameAware, BeanClassLoaderAware, BeanFactoryAware……的作用就是给对应的Bean回设这个Bean想知道的信息。

而这里的有个小疑问：为什么第十个执行的Bean没执行呢？而想象之中第十一个执行的方法在第十三个方法之后执行呢？

第一个问题是我们没有对应的Servlet。

第二个问题：其实BeanPostProcessor是一个对所有Bean都会拦截的方法，如果我们想要在这个bean之前执行，我们需要在context的refresh阶段之前添加进去而不是通过bean注册进去，我们通过另外一种方式试试。

<span style="color:#000000"><code class="language-java"><span style="color:#6679cc">public</span> <span style="color:#6679cc">static</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">main</span><span style="color:#999999">(</span>String<span style="color:#999999">[</span><span style="color:#999999">]</span> args<span style="color:#999999">)</span> <span style="color:#999999">{</span>AnnotationConfigApplicationContext context <span style="color:#ac9739">=</span> <span style="color:#6679cc">new</span> AnnotationConfigApplicationContext<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>context<span style="color:#999999">.</span><span style="color:#3d8fd1">getBeanFactory</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#3d8fd1">addBeanPostProcessor</span><span style="color:#999999">(</span><span style="color:#6679cc">new</span> BeanLifecycle<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">)</span><span style="color:#999999">;</span>context<span style="color:#999999">.</span><span style="color:#3d8fd1">register</span><span style="color:#999999">(</span>BeanLifecycle<span style="color:#999999">.</span><span style="color:#6679cc">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>context<span style="color:#999999">.</span><span style="color:#3d8fd1">refresh</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>context<span style="color:#999999">.</span><span style="color:#3d8fd1">getBean</span><span style="color:#999999">(</span>BeanLifecycle<span style="color:#999999">.</span><span style="color:#6679cc">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
</code></span>

output如下：

<span style="color:#000000"><code>22:34:48.200 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
第十一个执行 postProcessBeforeInitialization bean =
第十一个执行 postProcessBeforeInitialization beanName =
第十四个执行 postProcessAfterInitialization bean =
第十四个执行 postProcessAfterInitialization beanName =
22:34:48.227 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
第十一个执行 postProcessBeforeInitialization bean =
第十一个执行 postProcessBeforeInitialization beanName =
第十四个执行 postProcessAfterInitialization bean =
第十四个执行 postProcessAfterInitialization beanName =
22:34:48.229 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
第十一个执行 postProcessBeforeInitialization bean =
第十一个执行 postProcessBeforeInitialization beanName =
第十四个执行 postProcessAfterInitialization bean =
第十四个执行 postProcessAfterInitialization beanName =
22:34:48.230 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
第十一个执行 postProcessBeforeInitialization bean =
第十一个执行 postProcessBeforeInitialization beanName =
第十四个执行 postProcessAfterInitialization bean =
第十四个执行 postProcessAfterInitialization beanName =
22:34:48.232 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
第十一个执行 postProcessBeforeInitialization bean =
第十一个执行 postProcessBeforeInitialization beanName =
第十四个执行 postProcessAfterInitialization bean =
第十四个执行 postProcessAfterInitialization beanName =
22:34:48.235 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'beanLifecycle'
第一个执行 bean name =
第二个执行  classLoader =
第三个执行 beanFactory =
第十一个执行 postProcessBeforeInitialization bean =
第十一个执行 postProcessBeforeInitialization beanName =
第四个执行 environment =
第五个执行 resolver =
第六个执行 resourceLoader =
第七个执行 applicationEventPublisher =
第八个执行 messageSource =
第九个执行 applicationContext =
第十二个执行 = afterPropertiesSet
第十四个执行 postProcessAfterInitialization bean =
第十四个执行 postProcessAfterInitialization beanName =
</code></span>

为什么上面的postProcessAfterInitialization方法执行了好多次呢？

我们看看 BeanPostProcessor 的postProcessBeforeInitialization方法的注解：

Apply this BeanPostProcessor to the given new bean instance before any bean initialization callbacks (like InitializingBean’s afterPropertiesSet
or a custom init-method). The bean will already be populated with property values. The returned bean instance may be a wrapper around the original.

大意就是：这个方法会被每个bean 初始化之前都会回调这个方法，比如会在InitializingBean’s afterPropertiesSet或bean自定义的一个init-method方法调用之前回调这个方法。

然后看看postProcessAfterInitialization 的注解：

Apply this BeanPostProcessor to the given new bean instance after any bean initialization callbacks (like InitializingBean’s afterPropertiesSet or a custom init-method). The bean will already be populated with property values. The returned bean instance may be a wrapper around the original.

大意就是：这个方法会在每个bean初始化之后都会回调这个方法。

这样就解释了为什么的 postProcessBeforeInitialization 和 postProcessAfterInitialization 方法会被打印这么多次，因为它是每个bean被初始化一次，它都会被调用一次。那么我设想是不是在需要对某些 bean，或者是底层接口的一个bean，我想拦截下来并且做一点修饰，这样就不需要入侵到底层代码里面去了。

然后看了下 BeanPostProcessor 的注解：

Factory hook that allows for custom modification of new bean instances — for example, checking for marker interfaces or wrapping beans with proxies.

大意就是：Factory的hook（钩子方法），可以定制修改一个新的bean实例，比如检查interfaces的创建条件对不对，使用代理包装某个beans。

不过上面有个结果比较奇怪：为什么的postProcessBeforeInitialization 会在 EnvironmentAware之前执行。这个挖个坑，后面地细细研究一下。

这里给大家一个我使用BeanPostProcessor的例子。

<span style="color:#000000"><code class="language-java"><span style="color:#999999">@Configuration</span>
<span style="color:#6679cc">public</span> <span style="color:#6679cc">class</span> MysqlConfigAdapter <span style="color:#6679cc">implements</span> BeanPostProcessor<span style="color:#999999">{</span><span style="color:#999999">@Value</span><span style="color:#999999">(</span><span style="color:#ac9739">"mysql.username"</span><span style="color:#999999">)</span><span style="color:#6679cc">private</span> String username<span style="color:#999999">;</span><span style="color:#999999">@Value</span><span style="color:#999999">(</span><span style="color:#ac9739">"mysql.password"</span><span style="color:#999999">)</span><span style="color:#6679cc">private</span> String password<span style="color:#999999">;</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> Object <span style="color:#3d8fd1">postProcessAfterInitialization</span><span style="color:#999999">(</span>Object bean<span style="color:#999999">,</span> String beanName<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span><span style="color:#6679cc">if</span> <span style="color:#999999">(</span>bean <span style="color:#6679cc">instanceof</span> XxxDatabase<span style="color:#999999">)</span> <span style="color:#999999">{</span><span style="color:#999999">(</span><span style="color:#999999">(</span>XxxDatabase<span style="color:#999999">)</span>bean<span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#3d8fd1">setUsername</span><span style="color:#999999">(</span>username<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">(</span><span style="color:#999999">(</span>XxxDatabase<span style="color:#999999">)</span>bean<span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#3d8fd1">setPassword</span><span style="color:#999999">(</span>password<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#6679cc">return</span> bean<span style="color:#999999">;</span><span style="color:#999999">}</span><span style="color:#999999">@Override</span><span style="color:#6679cc">public</span> <span style="color:#6679cc">void</span> <span style="color:#3d8fd1">setApplicationContext</span><span style="color:#999999">(</span>ApplicationContext applicationContext<span style="color:#999999">)</span> <span style="color:#6679cc">throws</span> BeansException <span style="color:#999999">{</span><span style="color:#6679cc">this</span><span style="color:#999999">.</span>applicationContext <span style="color:#ac9739">=</span> applicationContext<span style="color:#999999">;</span><span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span>

上面的例子是本人在实际生产运用中使用到的例子（改造过），当时是因为使用了第三方中间件，而为了能让第三方中间件接入配置中心（比如阿波罗，nacos），而不侵入对方的代码，就在外层写了个适配器（适配器模式）。拦截下对应的bean，并且修改里面的值，再给出去。恰好符合注解讲的那样：The returned bean instance may be a wrapper around the original.

除了上面的例子之外，我们再说一点BeanPostProcessor的两个注意事项：

注册方式：BeanPostProcessor可以直接被ApplicationContext发现，也可以手动通过BeanFactory注册。
顺序：有多个BeanPostProcessor的时候，通过ApplicationContext发现的就会看这个bean是否implement了PriorityOrdered和Ordered接口，按照这两个的顺序来排序（PriorityOrdered优先于Ordered）。如果是通过手动注册来的，就会忽略掉这些属性，只看添加的顺序来决定先后顺序。最后@Order是无效的，目前还没有实现（5.3.0-SNAPSHOT）版本。

BeanFactoryPostProcessor

PostProcessor 其实除了这个BeanPostProcessor 之外，之前看源码的时候也注意到了有另外一个：BeanFactoryPostProcessor。然后我们看看BeanFactoryPostProcessor 源码注解解释。

Factory hook that allows for custom modification of an application context’s bean definitions, adapting the bean property values of the context’s underlying bean factory.

大意就是说：这是要给针对BeanFactory的钩子方法，是一个可以对applicationContext的BeanFactory修改的方法。修改这个context的beanfactory的properties value。这个权限非常大。

它的注册方式也分两种：通过applicationContext自动探测，通过ConfigurableApplicationContext.addBeanFactoryPostProcessor手动注册。
它的顺序性和BeanPostProcessor一样

其实BeanFactoryPostProcessor 是要给非常强大的接口，我们的@Configuration功能，SpringBoot的自动装配还有Spring-Mybatis的适配都是靠这个来实现的。具体的实现可以参考ConfigurationClassPostProcessor ，如果后面有机会，可以再给大家看看ConfigurationClassPostProcessor它的实现。（再挖个坑。）

BeanFactoryPostProcessor 和BeanPostProcessor有个很大的区别是：BeanFactoryPostProcessor 的执行时机很早，在所有的bean初始化包括那些aware赋值之前就执行了，而BeanPostProcessor是每个bean初始化之前执行postProcessBeforeInitialization，初始化之后执行postProcessAfterInitialization。

好了，这期就到这里了。

那么我们把各种各样的Aware看做一个阶段，我们是否可以得出这样的结论：

<span style="color:#000000"><code>BeanFactoryPostProcessor.postProcessBeanFactory -->
Aware -->
BeanPostProcessor.postProcessBeforeInitialization -->
initialBean -->
initMethod -->
BeanPostProcessor.postProcessAfterInitialization -->
DisposableBean -->
destroyMethod</code></span>