Spring擴展點之Aware介面族
- 2019 年 10 月 4 日
- 筆記
Spring中提供了各種Aware介面，方便從上下文中獲取當前的運行環境，比較常見的幾個子介面有：BeanFactoryAware,BeanNameAware,ApplicationContextAware,EnvironmentAware，BeanClassLoaderAware等
這些Aware的作用都可以從命名得知
Aware的處理
其中BeanNameAware、BeanClassLoaderAware和BeanFactoryAware這三個是直接在bean的初始化之前就處理了的，具體程式碼在AbstractAutowireCapableBeanFactory.initializeBean方法中：
protected Object initializeBean(String beanName, Object bean, RootBeanDefinition mbd) { // 判斷對象實現的介面類型，處理特定的三種介面類型：BeanNameAware、BeanClassLoaderAware和BeanFactoryAware。 if (bean instanceof BeanNameAware) { ((BeanNameAware) bean).setBeanName(beanName); } if (bean instanceof BeanClassLoaderAware) { ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader()); } if (bean instanceof BeanFactoryAware) { ((BeanFactoryAware) bean).setBeanFactory(this); } // 開始Bean初始化前處理、初始化、初始化後處理 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); } return wrappedBean; }
除了這三種之外的那些Aware介面的實現就不太一樣了，它們都是利用BeanPostProcessor介面完成的，關於BeanPostProcessor介面的原理可以這篇文章：Spring擴展點之BeanPostProcessor
如ApplicationContextAware就是利用ApplicationContextAwareProcessor實現的：
public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException { AccessControlContext acc = null; if (System.getSecurityManager() != null && (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware || bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware || bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) { acc = this.applicationContext.getBeanFactory().getAccessControlContext(); } if (acc != null) { AccessController.doPrivileged((PrivilegedAction<Object>) () -> { //具體實現 invokeAwareInterfaces(bean); return null; }, acc); } else { //具體實現 invokeAwareInterfaces(bean); } return bean; } 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); } } }
而ApplicationContextAwareProcessor的註冊奧秘在AbstractApplicationContext.prepareBeanFactory方法中：
beanFactory.setBeanClassLoader(getClassLoader()); beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this)); beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class); beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class); beanFactory.ignoreDependencyInterface(MessageSourceAware.class); beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
