Spring注解驱动开发之七——BeanPostProcessor 执行原理、在spring 中的应用
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）断点查看代码 1.在MyBeanPostProcessor添加断点，运行测试方法通过观察栈，查看执行流程 下方长长的英文是调试中右下角的窗口： 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 getBean(beanName); 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; } 2） 总结 运行过程中的执行原理 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 @ComponentpublicclassDogimplementsApplicationContextAware{ private ApplicationContext applicationContext; public Dog(){ System.out.println("dog constructor..."); } @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { // TODO Auto-generated method stub 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; } -END- 可以关注我的公众号，免费获取价值1980元学习资料 点击“在看”，学多少都不会忘~ 本文分享自微信公众号 - 阿聪的全栈之路（gh_ffab7c84fb0c）。如有侵权，请联系 support@oschina.cn 删除。本文参与“OSC源创计划”，欢迎正在阅读的你也加入，一起分享。
