目录1. 简单认识BeanProcessorBeanProcessor的理解一个BeanProcessor的使用实例2. BeanProcessor的实现思路和简化实例BeanProcessor大概的实现思路一个BeanProcessor的简化逻辑实例net.postProcessor.PostProcessor.java3. spring中BeanProcessor的源码解析
1. 简单认识BeanProcessor
BeanProcessor的理解
BeanProcessor是spring中的一个重要接口，他有两个接口方法一个是postProcessBeforeInitialization前置初始化，另一个是postProcessAfterInitialization后置初始化。从名称上就可以大概清楚这个接口的作用：在一个业务流程的前后加入两个接口方法，当执行这个业务流程时，就会触发这两个接口方法的执行。简单的总结一下有两个要点：
- 在业务流程中，根据BeanProcessor接口方法加在不同的位置(一般是前后)，可以实现对业务逻辑的扩展。 在业务逻辑执行前，BeanProcessor的实现类必须已经被创建完成(BeanProcessor接口类必须要优先实例化)。
而在spring中，就有很多实现了BeanProcessor的bean，通过在重要的业务流程(如bean的生命周期流程)的前后加上BeanProcessor接口方法，就可以对业务逻辑进行修改或补充。
一个BeanProcessor的使用实例
在spring的bean生命周期中，BeanProcessor接口方法会在bean创建后的初始化方法(init-method或@PostConstruct指向的方法)前后执行before和after方法；那有没有在bean创建前后执行的接口方法呢？答案是肯定有的，这个功能是由BeanProcessor的子接口InstantiationAwareBeanPostProcessor来实现的，他也是有before和after方法，会在bean实例化前后执行。
我们先定义一个BeanProcessor接口实现类和一个InstantiationAwareBeanPostProcessor接口实现类。
BeanPostProcessor实现类:
//net.postProcessor.CustomerPostProcessor@Componentpublic class CustomerPostProcessor implements BeanPostProcessor { @PostConstruct public void init(){ System.out.println("执行CustomerPostProcessor的PostConstruct"); } public CustomerPostProcessor(){ System.out.println("执行CustomerPostProcessor的构造方法"); } @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实现类:
//net.postProcessor.CustomerInitialPostProcessor@Componentpublic class CustomerInitialPostProcessor implements InstantiationAwareBeanPostProcessor { @PostConstruct public void init(){ System.out.println("执行CustomerInitialPostProcessor的PostConstruct"); } public CustomerInitialPostProcessor(){ System.out.println("执行CustomerInitialPostProcessor的构造方法"); } @Override public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException { System.out.println("bean初始化前执行：class为"+beanClass.getName()+"|beanName为"+beanName); return null; } @Override public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException { System.out.println("bean初始化后执行：Object为"+bean+"|beanName为"+beanName); return false; }}
再创建一个普通的bean对象：
//net.postProcessor.FirstBean@Componentpublic class FirstBean implements InitializingBean { private String msg = "hello"; @PostConstruct public void init(){ System.out.println("执行FirstBean的PostConstruct"); } public FirstBean(){ System.out.println("FirstBean构造方法！"+msg); } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } @Override public void afterPropertiesSet() throws Exception { System.out.println("执行FirstBean的afterPropertiesSet"); }}
我们创建一个spring工厂对象将上述bean加载进去：
@Testpublic void test(){ AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext("net.postProcessor");}//执行得到以下结果：执行CustomerInitialPostProcessor的构造方法执行CustomerInitialPostProcessor的PostConstruct执行CustomerPostProcessor的构造方法执行CustomerPostProcessor的PostConstruct bean初始化前执行：class为net.postProcessor.FirstBean|beanName为firstBeanFirstBean构造方法！hellobean初始化后执行：Object为net.postProcessor.FirstBean@79179359|beanName为firstBean net.postProcessor.FirstBean@79179359======BeforeInitialization======firstBean执行FirstBean的PostConstruct执行FirstBean的afterPropertiesSetnet.postProcessor.FirstBean@79179359======AfterInitialization======firstBean
通过上述结果证明了我们之前的说法是正确的：
1.BeanPostProcessor接口类会优先实例化，且在实例化中无法不会调用BeanPostProcessor接口方法的
2.InstantiationAwareBeanPostProcessor接口方法会在FirstBean构造方法构造方法前后执行
3.BeanPostProcessor接口方法会在FirstBean实例化后进行初始化的前后执行
注意：若@PostConstruct注解方法方法未执行，请加入javax.annotation:javax.annotation-api:1.3.2jar包依赖，原因是@PostConstruct是J2EE标准的注解，不是spring自己的接口，而在JDK8往上的版本中设计者打算弃用这些注解，所以做了处理，我们是没有办法直接使用J2EE标准注解的(@Resource、@PostConstruct、@PreDestroy等几个注解)，为了兼容这种情况，所以有了javax.annotation-apijar包的产生(或者降低JDK版本)。
2. BeanProcessor的实现思路和简化实例
BeanProcessor大概的实现思路
通过之前的了解BeanProcessor的使用，我们可以知道BeanProcessor并不复杂，但是却十分的重要，下面来分析下BeanProcessor的实现思路：
- 创建个接口A，接口包含一些切点方法(Before、After、Around之类的)，实现这个接口A的类要在使用前就创建好 我们需要有个业务流程，这个业务流程由若干步组成；将接口A的接口方法插入到这些业务步骤之间(需要扩展的地方) 要执行这个业务流程时，把接口A的实现类对象赋值到业务流程中，在执行业务流程中，就会触发接口方法的执行完成功能扩展
当我们更换赋值到业务流程中的接口A的实现类时，对应的扩展逻辑也会随之变化，这样就实现了可插拔式的扩展逻辑(策略模式)。
一个BeanProcessor的简化逻辑实例
在spring中我们可以创建任意数量的bean实现BeanProcessor接口，所以实际上我们是要一个全局的beanProcessorList对象用来存储这些BeanProcessor对象；在执行业务代码时，要循环这个beanProcessorList对象，获取你需要的BeanProcessor对象来执行接口方法。下面是一个模拟spring bean生命周期的简化版，来帮助你理解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构造方法！"+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("执行CustomerPostProcessor的PostConstruct"); } public CustomerPostProcessor(){ System.out.println("执行CustomerPostProcessor的构造方法"); } @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 { //模拟扫描到的bean信息<"SecondBean", "net.postProcessor.SecondBean"> Map<String, String> scanBeanMap = new HashMap<>(); //模拟spring的beanPostProcessors列表 List<BeanPostProcessor> processorBeanList = new ArrayList<>(); //模拟bean对象缓存 Map<String, Object> beanCache = new HashMap<>(); //添加扫描的bean信息 public PostProcessor addBeanInfo(String beanName, String classPath){ this.scanBeanMap.put(beanName, classPath); return this; } //模拟bean创建流程 public Object execute(){ try { //先临时存储实现了postProcessor接口的bean对象 List<BeanPostProcessor> postProcessorStrList = new ArrayList<>(); //循环scanBeanMap，获取bean列表中实现了postProcessor接口的类，加入processorBeanList中 for(String temp: scanBeanMap.keySet()){ Class<?> clazz = Class.forName(scanBeanMap.get(temp)); //判断是否实现了BeanPostProcessor接口 if(BeanPostProcessor.class.isAssignableFrom(clazz)){ //实例化让如临时容器 postProcessorStrList.add((BeanPostProcessor)createBean(temp)); } } //将实现了postProcessor接口的bean加入processorBeanList中 for(BeanPostProcessor obj: postProcessorStrList){ processorBeanList.add(obj); } //再次循环scanBeanMap初始化所用bean for(String temp: scanBeanMap.keySet()){ createBean(temp); } } catch (ClassNotFoundException e) { e.printStackTrace(); } return null; } //bean实例化 public Object createBean(String beanName){ //从缓存中获取 if(beanCache.containsKey(beanName)){ return beanCache.get(beanName); }else{ //缓存中取不到，则进行创建后加入缓存 try { Class<?> clazz = Class.forName(scanBeanMap.get(beanName)); //processor前置方法执行 for(BeanPostProcessor processor : processorBeanList){ processor.postProcessBeforeInitialization(clazz, beanName); } //bean实例化 Object result = clazz.getConstructor().newInstance(); //processor后置方法执行 for(BeanPostProcessor processor : processorBeanList){ processor.postProcessAfterInitialization(result, beanName); } //将bean加入缓存 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; }}
代码调用
public static void main(String[] args) { PostProcessor postProcessor = new PostProcessor(); //添加扫描到的bean postProcessor .addBeanInfo("SecondBean", "net.postProcessor.SecondBean") .addBeanInfo("CustomerPostProcessor", "net.postProcessor.CustomerPostProcessor"); postProcessor.execute();}//执行结果执行CustomerPostProcessor的构造方法class net.postProcessor.SecondBean======BeforeInitialization======SecondBeanSecondBean构造方法！worldnet.postProcessor.SecondBean@1b40d5f0======AfterInitialization======SecondBean
代码逻辑如下：
- 循环bean信息列表，将BeanPostProcessor接口bean分离出来优先实例化(实例化中缓存bean对象)，并将之放入临时容器。 循环完成，将临时容器中的BeanPostProcessor接口bean赋值到全局BeanPostProcessor接口列表中 再次循环bean信息列表，缓存存在则直接返回缓存对象，不存在则进行bean实例化，期间循环调用全局BeanPostProcessor接口对象方法
3. spring中BeanProcessor的源码解析
我们要从spring中的refresh()开始看起：
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. //刷新准备 prepareRefresh(); // Tell the subclass to refresh the internal bean factory. //告诉子类刷新内部bean工厂。 ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. //为容器准备bean工程 prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. //允许在上下文bean的后处理工厂子类。 postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. //优先将BeanDefinitionRegistryPostProcessor\BeanFactoryPostProcessor接口的bean对象实例化 //属于spring内部组件调用 invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. //处理用户自定义PostProcessor接口对象，之后加入spring的beanPostProcessors列表， // 供之后预实例化其他bean时触发这些PostProcessor方法 registerBeanPostProcessors(beanFactory);//...省略代码 //实例化所有(non-lazy-init)单件。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销毁 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... //重置公共缓存 resetCommonCaches(); } }}
其中包含有postProcess字段都有可能和BeanProcessor相关，这里有三个相关方法：
- postProcessBeanFactory(beanFactory)，这个是一共空的扩展方法，显然无关 invokeBeanFactoryPostProcessors(beanFactory)，处理spring中实现了BeanProcessor接口的内部组件直接调用接口方法 registerBeanPostProcessors(beanFactory)，实例化用户自定义BeanProcessor接口bean组件，之后循环赋值到全局BeanProcessor列表中
所以registerBeanPostProcessors()就是我们要找的对象，来跟进看下registerBeanPostProcessors()：
//AbstractApplicationContext#registerBeanPostProcessorsprotected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) { //委托给PostProcessorRegistrationDelegate.registerBeanPostProcessors进行处理PostProcessorRegistrationDelegate.registerBeanPostProcessors进行处理(beanFactory, this);}
public static void registerBeanPostProcessors( ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) { //查询实现了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<>(); //根据beanName循环调用getBean进行实例化 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. //对BeanPostProcessor接口对象进行排序 sortPostProcessors(priorityOrderedPostProcessors, beanFactory); //将获取到的PostProcessors接口对象加入到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));}
果然这里就是处理BeanPostProcessor接口的地方，逻辑和之前的思路类似：
- 循环扫描到的bean列表，获取实现了BeanPostProcessor接口的beanName数组 循环beanName数组数组，调用beanFactory.getBean()将bean实例化，并放入priorityOrderedPostProcessors列表中 调用sortPostProcessors对priorityOrderedPostProcessors列表进行排序(处理BeanPostProcessor调用的顺序) 调用registerBeanPostProcessors将priorityOrderedPostProcessors列表中的bean对象赋值到全局列表beanPostProcessors中 回到refresh()中，当调用finishBeanFactoryInitialization()对所用bean进行预实例化时就会调用这些BeanPostProcessor接口方法
以上就是spring BeanProcessor接口详解的详细内容，更多关于spring BeanProcessor接口的资料请关注其它相关文章！
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