spring BeanProcessor接口詳解
BeanProcessor是spring中的一個重要接口，他有兩個接口方法一個是postProcessBeforeInitialization前置初始化，另一個是postProcessAfterInitialization后置初始化。從名稱上就可以大概清楚這個接口的作用：在一個業務流程的前后加入兩個接口方法，當執行這個業務流程時，就會觸發這兩個接口方法的執行。簡單的總結一下有兩個要點：
在業務流程中，根據BeanProcessor接口方法加在不同的位置(一般是前后)，可以實現對業務邏輯的擴展。 在業務邏輯執行前，BeanProcessor的實現類必須已經被創建完成(BeanProcessor接口類必須要優先實例化)。而在spring中，就有很多實現了BeanProcessor的bean，通過在重要的業務流程(如bean的生命周期流程)的前后加上BeanProcessor接口方法，就可以對業務邏輯進行修改或補充。
一個BeanProcessor的使用實例在spring的bean生命周期中，BeanProcessor接口方法會在bean創建后的初始化方法(init-method或@PostConstruct指向的方法)前后執行before和after方法；那有沒有在bean創建前后執行的接口方法呢？答案是肯定有的，這個功能是由BeanProcessor的子接口InstantiationAwareBeanPostProcessor來實現的，他也是有before和after方法，會在bean實例化前后執行。
我們先定義一個BeanProcessor接口實現類和一個InstantiationAwareBeanPostProcessor接口實現類。
BeanPostProcessor實現類:
//net.postProcessor.CustomerPostProcessor@Componentpublic class CustomerPostProcessor implements BeanPostProcessor { @PostConstruct public void init(){ System.out.println('執行CustomerPostProcessor的PostConstruct'); } public CustomerPostProcessor(){ System.out.println('執行CustomerPostProcessor的構造方法'); } @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.out.println(bean+'======BeforeInitialization======'+ beanName); return bean; } @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println(bean+'======AfterInitialization======'+ beanName); return bean; }}
InstantiationAwareBeanPostProcessor實現類:
//net.postProcessor.CustomerInitialPostProcessor@Componentpublic class CustomerInitialPostProcessor implements InstantiationAwareBeanPostProcessor { @PostConstruct public void init(){ System.out.println('執行CustomerInitialPostProcessor的PostConstruct'); } public CustomerInitialPostProcessor(){ System.out.println('執行CustomerInitialPostProcessor的構造方法'); } @Override public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException { System.out.println('bean初始化前執行：class為'+beanClass.getName()+'|beanName為'+beanName); return null; } @Override public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException { System.out.println('bean初始化后執行：Object為'+bean+'|beanName為'+beanName); return false; }}
再創建一個普通的bean對象：
//net.postProcessor.FirstBean@Componentpublic class FirstBean implements InitializingBean { private String msg = 'hello'; @PostConstruct public void init(){ System.out.println('執行FirstBean的PostConstruct'); } public FirstBean(){ System.out.println('FirstBean構造方法！'+msg); } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } @Override public void afterPropertiesSet() throws Exception { System.out.println('執行FirstBean的afterPropertiesSet'); }}
我們創建一個spring工廠對象將上述bean加載進去：
@Testpublic void test(){ AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext('net.postProcessor');}//執行得到以下結果：執行CustomerInitialPostProcessor的構造方法執行CustomerInitialPostProcessor的PostConstruct執行CustomerPostProcessor的構造方法執行CustomerPostProcessor的PostConstruct bean初始化前執行：class為net.postProcessor.FirstBean|beanName為firstBeanFirstBean構造方法！hellobean初始化后執行：Object為net.postProcessor.FirstBean@79179359|beanName為firstBean net.postProcessor.FirstBean@79179359======BeforeInitialization======firstBean執行FirstBean的PostConstruct執行FirstBean的afterPropertiesSetnet.postProcessor.FirstBean@79179359======AfterInitialization======firstBean
通過上述結果證明了我們之前的說法是正確的：
1.BeanPostProcessor接口類會優先實例化，且在實例化中無法不會調用BeanPostProcessor接口方法的
2.InstantiationAwareBeanPostProcessor接口方法會在FirstBean構造方法構造方法前后執行
3.BeanPostProcessor接口方法會在FirstBean實例化后進行初始化的前后執行
注意：若@PostConstruct注解方法方法未執行，請加入javax.annotation:javax.annotation-api:1.3.2jar包依賴，原因是@PostConstruct是J2EE標準的注解，不是spring自己的接口，而在JDK8往上的版本中設計者打算棄用這些注解，所以做了處理，我們是沒有辦法直接使用J2EE標準注解的(@Resource、@PostConstruct、@PreDestroy等幾個注解)，為了兼容這種情況，所以有了javax.annotation-apijar包的產生(或者降低JDK版本)。
通過之前的了解BeanProcessor的使用，我們可以知道BeanProcessor并不復雜，但是卻十分的重要，下面來分析下BeanProcessor的實現思路：
創建個接口A，接口包含一些切點方法(Before、After、Around之類的)，實現這個接口A的類要在使用前就創建好 我們需要有個業務流程，這個業務流程由若干步組成；將接口A的接口方法插入到這些業務步驟之間(需要擴展的地方) 要執行這個業務流程時，把接口A的實現類對象賦值到業務流程中，在執行業務流程中，就會觸發接口方法的執行完成功能擴展當我們更換賦值到業務流程中的接口A的實現類時，對應的擴展邏輯也會隨之變化，這樣就實現了可插拔式的擴展邏輯(策略模式)。
一個BeanProcessor的簡化邏輯實例在spring中我們可以創建任意數量的bean實現BeanProcessor接口，所以實際上我們是要一個全局的beanProcessorList對象用來存儲這些BeanProcessor對象；在執行業務代碼時，要循環這個beanProcessorList對象，獲取你需要的BeanProcessor對象來執行接口方法。下面是一個模擬spring bean生命周期的簡化版，來幫助你理解spring中BeanProcessor的工作原理。
net.postProcessor.SecondBean.java
@Componentpublic class SecondBean { private String msg = 'world'; public SecondBean(){ System.out.println('SecondBean構造方法！'+msg); } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; }}
net.postProcessor.CustomerPostProcessor.java
@Componentpublic class CustomerPostProcessor implements BeanPostProcessor { @PostConstruct public void init(){ System.out.println('執行CustomerPostProcessor的PostConstruct'); } public CustomerPostProcessor(){ System.out.println('執行CustomerPostProcessor的構造方法'); } @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { System.out.println(bean+'======BeforeInitialization======'+ beanName); return bean; } @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println(bean+'======AfterInitialization======'+ beanName); return bean; }}net.postProcessor.PostProcessor.java
public class PostProcessor { //模擬掃描到的bean信息<'SecondBean', 'net.postProcessor.SecondBean'> Map<String, String> scanBeanMap = new HashMap<>(); //模擬spring的beanPostProcessors列表 List<BeanPostProcessor> processorBeanList = new ArrayList<>(); //模擬bean對象緩存 Map<String, Object> beanCache = new HashMap<>(); //添加掃描的bean信息 public PostProcessor addBeanInfo(String beanName, String classPath){ this.scanBeanMap.put(beanName, classPath); return this; } //模擬bean創建流程 public Object execute(){ try { //先臨時存儲實現了postProcessor接口的bean對象 List<BeanPostProcessor> postProcessorStrList = new ArrayList<>(); //循環scanBeanMap，獲取bean列表中實現了postProcessor接口的類，加入processorBeanList中 for(String temp: scanBeanMap.keySet()){ Class<?> clazz = Class.forName(scanBeanMap.get(temp)); //判斷是否實現了BeanPostProcessor接口 if(BeanPostProcessor.class.isAssignableFrom(clazz)){//實例化讓如臨時容器postProcessorStrList.add((BeanPostProcessor)createBean(temp)); } } //將實現了postProcessor接口的bean加入processorBeanList中 for(BeanPostProcessor obj: postProcessorStrList){ processorBeanList.add(obj); } //再次循環scanBeanMap初始化所用bean for(String temp: scanBeanMap.keySet()){ createBean(temp); } } catch (ClassNotFoundException e) { e.printStackTrace(); } return null; } //bean實例化 public Object createBean(String beanName){ //從緩存中獲取 if(beanCache.containsKey(beanName)){ return beanCache.get(beanName); }else{ //緩存中取不到，則進行創建后加入緩存 try { Class<?> clazz = Class.forName(scanBeanMap.get(beanName)); //processor前置方法執行 for(BeanPostProcessor processor : processorBeanList){processor.postProcessBeforeInitialization(clazz, beanName); } //bean實例化 Object result = clazz.getConstructor().newInstance(); //processor后置方法執行 for(BeanPostProcessor processor : processorBeanList){processor.postProcessAfterInitialization(result, beanName); } //將bean加入緩存 beanCache.put(beanName, result); return result; } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InstantiationException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } catch (InvocationTargetException e){ e.printStackTrace(); } } return null; }}
代碼調用
public static void main(String[] args) { PostProcessor postProcessor = new PostProcessor(); //添加掃描到的bean postProcessor .addBeanInfo('SecondBean', 'net.postProcessor.SecondBean') .addBeanInfo('CustomerPostProcessor', 'net.postProcessor.CustomerPostProcessor'); postProcessor.execute();}//執行結果執行CustomerPostProcessor的構造方法class net.postProcessor.SecondBean======BeforeInitialization======SecondBeanSecondBean構造方法！worldnet.postProcessor.SecondBean@1b40d5f0======AfterInitialization======SecondBean
代碼邏輯如下：
循環bean信息列表，將BeanPostProcessor接口bean分離出來優先實例化(實例化中緩存bean對象)，并將之放入臨時容器。 循環完成，將臨時容器中的BeanPostProcessor接口bean賦值到全局BeanPostProcessor接口列表中 再次循環bean信息列表，緩存存在則直接返回緩存對象，不存在則進行bean實例化，期間循環調用全局BeanPostProcessor接口對象方法3. spring中BeanProcessor的源碼解析我們要從spring中的refresh()開始看起：
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //刷新準備 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. //告訴子類刷新內部bean工廠。 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //為容器準備bean工程 prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. //允許在上下文bean的后處理工廠子類。 postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //優先將BeanDefinitionRegistryPostProcessorBeanFactoryPostProcessor接口的bean對象實例化 //屬于spring內部組件調用 invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. //處理用戶自定義PostProcessor接口對象，之后加入spring的beanPostProcessors列表， // 供之后預實例化其他bean時觸發這些PostProcessor方法 registerBeanPostProcessors(beanFactory);//...省略代碼 //實例化所有(non-lazy-init)單件。finishBeanFactoryInitialization(beanFactory); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn('Exception encountered during context initialization - ' + 'cancelling refresh attempt: ' + ex); } // Destroy already created singletons to avoid dangling resources. //bean銷毀 destroyBeans(); // Reset ’active’ flag. //取消刷新 cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring’s core, since we // might not ever need metadata for singleton beans anymore... //重置公共緩存 resetCommonCaches(); } }}
其中包含有postProcess字段都有可能和BeanProcessor相關，這里有三個相關方法：
postProcessBeanFactory(beanFactory)，這個是一共空的擴展方法，顯然無關 invokeBeanFactoryPostProcessors(beanFactory)，處理spring中實現了BeanProcessor接口的內部組件直接調用接口方法 registerBeanPostProcessors(beanFactory)，實例化用戶自定義BeanProcessor接口bean組件，之后循環賦值到全局BeanProcessor列表中所以registerBeanPostProcessors()就是我們要找的對象，來跟進看下registerBeanPostProcessors()：
//AbstractApplicationContext#registerBeanPostProcessorsprotected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) { //委托給PostProcessorRegistrationDelegate.registerBeanPostProcessors進行處理PostProcessorRegistrationDelegate.registerBeanPostProcessors進行處理(beanFactory, this);}
public static void registerBeanPostProcessors( ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { //查詢實現了BeanPostProcessor接口的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. List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>(); List<BeanPostProcessor> internalPostProcessors = new ArrayList<>(); List<String> orderedPostProcessorNames = new ArrayList<>(); List<String> nonOrderedPostProcessorNames = new ArrayList<>(); //根據beanName循環調用getBean進行實例化 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. //對BeanPostProcessor接口對象進行排序 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); //將獲取到的PostProcessors接口對象加入到spring的beanPostProcessors列表 registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors); // Next, register the BeanPostProcessors that implement Ordered. 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. 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. 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));}
果然這里就是處理BeanPostProcessor接口的地方，邏輯和之前的思路類似：
循環掃描到的bean列表，獲取實現了BeanPostProcessor接口的beanName數組 循環beanName數組數組，調用beanFactory.getBean()將bean實例化，并放入priorityOrderedPostProcessors列表中 調用sortPostProcessors對priorityOrderedPostProcessors列表進行排序(處理BeanPostProcessor調用的順序) 調用registerBeanPostProcessors將priorityOrderedPostProcessors列表中的bean對象賦值到全局列表beanPostProcessors中 回到refresh()中，當調用finishBeanFactoryInitialization()對所用bean進行預實例化時就會調用這些BeanPostProcessor接口方法以上就是spring BeanProcessor接口詳解的詳細內容，更多關于spring BeanProcessor接口的資料請關注好吧啦網其它相關文章！
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