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本文包含以下内容：
BeanPostProcessor 执行原理
断点查看
总结运行过程中的执行原理
BeanPostProcessor 在spring 中的应用
ApplicationContextAwareProcessor 帮助组件注入IOC 容器
InitDestroyAnnotationBeanPostProcessor 用于处理 @PostConstruct 、@PreDestroy 注解
BeanValidationPostProcessor 数据校验
1.BeanPostProcessor 执行原理
1.在MyBeanPostProcessor添加断点，运行测试方法通过观察栈，查看执行流程
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2. <init>:84, AnnotationConfigApplicationContext 初始化容器
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) { this(); register(annotatedClasses); refresh(); }
3. refresh:543, AbstractApplicationContext 调用refresh() 函数 ,实例化所有剩余的单例
// Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory);
4 .finishBeanFactoryInitialization:867, AbstractApplicationContext
// Instantiate all remaining (non-lazy-init) singletons. beanFactory.preInstantiateSingletons();
preInstantiateSingletons:761, DefaultListableBeanFactory，具体通过getBean函数进行初始化剩余的Bean
5. doGetBean:302, AbstractBeanFactory 这一步 通过getSingleton 获取单实例， 通过初始化createBean 方法创建Bean
// Create bean instance. if (mbd.isSingleton()) { sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() { @Override public Object getObject() throws BeansException { try { return createBean(beanName, mbd, args); } catch (BeansException ex) { // Explicitly remove instance from singleton cache: It might have been put there // eagerly by the creation process, to allow for circular reference resolution. // Also remove any beans that received a temporary reference to the bean. destroySingleton(beanName); throw ex; } } }); bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd); }
6. createBean:483, AbstractAutowireCapableBeanFactory，调用初始化，获取Bean 实例
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
7. doCreateBean:555, AbstractAutowireCapableBeanFactory 进入到具体创建Bean 中 通过populateBean() 进行填充Bean 操作
Object exposedObject = bean; try { populateBean(beanName, mbd, instanceWrapper); if (exposedObject != null) { exposedObject = initializeBean(beanName, exposedObject, mbd); } }
8.最后可以看到 initializeBean:1620, AbstractAutowireCapableBeanFactory 中 执行 applyBeanPostProcessorsBeforeInitialization 和 applyBeanPostProcessorsAfterInitialization 进行 postProcessBeforeInitialization() 函数和postProcessAfterInitialization（） 函数的调用;中间调用 invokeInitMethods(beanName, wrappedBean, mbd) ;进行 初始化 函数的调用
Object wrappedBean = bean; if (mbd == null || !mbd.isSynthetic()) { wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName); }
try { invokeInitMethods(beanName, wrappedBean, mbd); } catch (Throwable ex) { throw new BeanCreationException( (mbd != null ? mbd.getResourceDescription() : null), beanName, "Invocation of init method failed", ex); }
if (mbd == null || !mbd.isSynthetic()) { wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName); }
9. applyBeanPostProcessorsBeforeInitialization:409,AbstractAutowireCapableBeanFactory 最后通过 getBeanPostProcessors() 扫描所有的 BeanPostProcessor 直到遇到null 进行返回退出循环
@Override public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName) throws BeansException {
Object result = existingBean; for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) { result = beanProcessor.postProcessBeforeInitialization(result, beanName); if (result == null) { return result; } } return result; }
通过查看断点调试结果， 可以看到，创建单例容器Bean 通过
populateBean（） 函数进行填充，invokeInitMethods(beanName, wrappedBean, mbd);
函数进行初始化，然后前后有applyBeanPostProcessorsBeforeInitialization 和applyBeanPostProcessorsAfterInitialization 进行对所有的BeanPostProcessor 扫描执行。
2.BeanPostProcessor 在spring 中的应用
在spring 中大量使用BeanPostProcessor ，进行处理，下面举例3个进行断点、代码测试:
1).ApplicationContextAwareProcessor 帮助组件注入IOC 容器
在Dog 中实现 implements ApplicationContextAware 接口，编写， setApplicationContext 将容器保存至属性方法中
@Componentpublic class Dog implements ApplicationContextAware { private ApplicationContext applicationContext;
public Dog(){ System.out.println("dog constructor..."); }
@Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.applicationContext = applicationContext; }}
1. postProcessBeforeInitialization:97,ApplicationContextAwareProcessor 可以看到 通过 postProcessBeforeInitialization 函数进行将容器进行赋值
2.通过invokeAwareInterfaces判断Bean 的类型进行类型转换，并进行赋值
private void invokeAwareInterfaces(Object bean) { if (bean instanceof Aware) { if (bean instanceof EnvironmentAware) { ((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment()); } if (bean instanceof EmbeddedValueResolverAware) { ((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver); } if (bean instanceof ResourceLoaderAware) { ((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext); } if (bean instanceof ApplicationEventPublisherAware) { ((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext); } if (bean instanceof MessageSourceAware) { ((MessageSourceAware) bean).setMessageSource(this.applicationContext); } if (bean instanceof ApplicationContextAware) { ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext); } } }
2).InitDestroyAnnotationBeanPostProcessor 用于处理 @PostConstruct 、@PreDestroy 注解。
查看 InitDestroyAnnotationBeanPostProcessor 源码， postProcessBeforeInitialization 函数代码，如下：
@Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass()); try { metadata.invokeInitMethods(bean, beanName); } catch (InvocationTargetException ex) { throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException()); } catch (Throwable ex) { throw new BeanCreationException(beanName, "Failed to invoke init method", ex); } return bean; }
使用 findLifecycleMetadata(bean.getClass()); 获取所有的生命周期函数，通过 metadata.invokeInitMethods(bean, beanName); 进行代理调用对应的生命周期函数
public void invokeInitMethods(Object target, String beanName) throws Throwable { Collection<LifecycleElement> initMethodsToIterate = (this.checkedInitMethods != null ? this.checkedInitMethods : this.initMethods); if (!initMethodsToIterate.isEmpty()) { boolean debug = logger.isDebugEnabled(); for (LifecycleElement element : initMethodsToIterate) { if (debug) { logger.debug("Invoking init method on bean '" + beanName + "': " + element.getMethod()); } element.invoke(target); } }}
3).BeanValidationPostProcessor 数据校验
用于进行数据校验，查看 BeanValidationPostProcessor 的源码 postProcessBeforeInitialization 和 postProcessAfterInitialization 代码如下，进行 doValidate（）函数进行数据校验。
@Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { if (!this.afterInitialization) { doValidate(bean); } return bean; }
@Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if (this.afterInitialization) { doValidate(bean); } return bean; }
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