BeanPostProcessor是處理bean的後置介面,beanDefinitionMaps中的BeanDefinition例項化完成後,完成populateBean,屬性設定,完成
初始化後,這個介面支援對bean做自定義的操作。
一:BeanPostProcessor的使用
定義一個測試用的model物件,name屬性預設為hello
public class BeanDemo { private String name = "hello"; public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { final StringBuffer sb = new StringBuffer("BeanDemo{"); sb.append("name='").append(name).append('\''); sb.append('}'); return sb.toString(); } }
自定義一個MyBeanPostProcessor類,實現BeanPostProcessor介面
@Service public class MyBeanPostProcessor implements BeanPostProcessor { public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { return null; } public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if(beanName.equals("beanDemo")){ BeanDemo beanDemo = (BeanDemo)bean; beanDemo.setName("kitty"); return beanDemo; } return bean; } }
從執行結果看,spring中維護的beanName為beanDemo的物件,name屬性為ketty
二:看看原始碼怎麼實現的
1:例項化並且註冊到beanPostProcessors集合中
主要的例項化邏輯在這個介面,這個介面的作用就是把所有實現BeanPostProcessor介面的類例項化,然後註冊到 beanPostProcessors這個快取中
public static void registerBeanPostProcessors( ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { // 獲取所有實現介面BeanPostProcessor的beanName String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false); // Register BeanPostProcessorChecker that logs an info message when // a bean is created during BeanPostProcessor instantiation, i.e. when // a bean is not eligible for getting processed by all BeanPostProcessors. int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length; beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)); // Separate between BeanPostProcessors that implement PriorityOrdered, // Ordered, and the rest. /** * 把實現PriorityOrdered 和 Ordered 和 其他的處理器分開 */ List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); List<BeanPostProcessor> internalPostProcessors = new ArrayList<>(); List<String> orderedPostProcessorNames = new ArrayList<>(); List<String> nonOrderedPostProcessorNames = new ArrayList<>(); /** * 1:遍歷集合postProcessorNames * 2:判斷型別,如果是PriorityOrdered,則例項化物件放入priorityOrderedPostProcessors集合, * Ordered 則放入orderedPostProcessorNames集合,其他的放入nonOrderedPostProcessorNames集合 */ for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); priorityOrderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessorNames.add(ppName); } else { nonOrderedPostProcessorNames.add(ppName); } } // First, register the BeanPostProcessors that implement PriorityOrdered. // 首先對priorityOrderedPostProcessors集合中例項物件排序,然後註冊,放入beanFactory中快取下來 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); // Next, register the BeanPostProcessors that implement Ordered. // 然後再例項化實現Ordered介面的物件,完成註冊 List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(); for (String ppName : orderedPostProcessorNames) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); orderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } sortPostProcessors(orderedPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, orderedPostProcessors); // Now, register all regular BeanPostProcessors. // 最後例項化什麼都沒有實現的,完成例項化並註冊 List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(); for (String ppName : nonOrderedPostProcessorNames) { BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class); nonOrderedPostProcessors.add(pp); if (pp instanceof MergedBeanDefinitionPostProcessor) { internalPostProcessors.add(pp); } } registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors); // Finally, re-register all internal BeanPostProcessors. // 最後再次註冊內部postProcessor sortPostProcessors(internalPostProcessors, beanFactory); registerBeanPostProcessors(beanFactory, internalPostProcessors); // Re-register post-processor for detecting inner beans as ApplicationListeners, // moving it to the end of the processor chain (for picking up proxies etc). beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext)); }
定義四類容器,高優先順序有序、有序、無序、內部
分類放入四種容器:
註冊BeanPostProcessor,將實現BeanPostProcessor介面的物件放入beanPostProcessors快取中
註冊完PriorityOrdered的實現類後,再處理Ordered的實現類
註冊什麼都沒有實現的BeanPostProcessor介面實現類,
最後註冊內部的BeanPostProcessor物件
到這裡BeanPostProcessor的例項化以及註冊工作完成,在beanFactory的beanPostProcessors集合中已經快取了所有的beanPostProcessor的物件
2:BeanPostProcessor的使用
因為這個介面是bean的後置介面,所以需要bean建立並初始化完成,才可以發揮作用,上一步的快取只是埋好點,以備使用,因為bean的例項化流程我們
還沒有分析,這裡直接看一下怎麼使用的
我們看一下init方法後的攔截,因為這個時候已經init完成,可以在後置介面中對bean做一下修改的操作
呼叫到我們自定義的MyBeanPostProcessor實現類:
把這個beanDemo物件屬性修改一下,修改完,再返回,將這個物件快取到spring的一級快取中。
總結:
BeanPostProcessor介面主要是對bean物件做一些自定義的操作,修改bean物件的資訊,aop代理也是通過這種方式實現的,
在refresh的registryBeanPostProcessor方法中例項化BeanPostProcessor物件,並且註冊到beanFactory容器的beanPostProcessors的快取中,
然後在後續的操作中攔截使用。