Spring源码学习--BeanPostProcessor

灰太狼 2022-06-16 13:58 189阅读 0赞

BeanPostProcessor接口的作用是在Spring容器完成Bean实例化前后可以添加一些自己的逻辑处理，我们可以定义一个或者多个BeanPostProcessor接口的实现。

BeanPostProcessor接口提供了两个方法：

1、postProcessBeforeInitialization  可以对Bean在实例化之前添加一些逻辑处理

2、postProcessAfterInitialization  可以对bean在实例化之后添加一些逻辑处理

public interface BeanPostProcessor {
    
    	//可以对Bean在实例化之前添加一些逻辑处理
    	Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
    
    	//可以对bean在实例化之后添加一些逻辑处理
    	Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
    
    }

简单示例MyBeanPostProcessor：

public class MyBeanPostProcessor implements BeanPostProcessor {
     
        //Bean 实例化之前进行的处理
        public Object postProcessBeforeInitialization(Object bean, String beanName)
               throws BeansException {
           System.out.println("对象" + beanName + "开始实例化");
           return bean;
        }
     
        //Bean 实例化之后进行的处理
        public Object postProcessAfterInitialization(Object bean, String beanName)
               throws BeansException {
           System.out.println("对象" + beanName + "实例化完成");
           return bean;
        }
    }

在applicationContext.xml中添加配置

#### 1、BeanPostProcessor保存到Spring容器 ####

这样MyBeanPostProcessor就会添加到Spring的容器中，在Spring容器中会将所有实现BeanPostProcessor的bean保存起来，具体实现在AbstractApplicationContext的registerBeanPostProcessors中

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    		//获取所有实现BeanPostProcessor的实现类
    		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    
    		
    		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    
    		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
    		List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
    		List<String> orderedPostProcessorNames = new ArrayList<String>();
    		List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    		for (String ppName : postProcessorNames) {
    			if (isTypeMatch(ppName, PriorityOrdered.class)) {
    				BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    				//保存所有的BeanPostProcessor
    				priorityOrderedPostProcessors.add(pp);
    				if (pp instanceof MergedBeanDefinitionPostProcessor) {
    					internalPostProcessors.add(pp);
    				}
    			}
    			else if (isTypeMatch(ppName, Ordered.class)) {
    				orderedPostProcessorNames.add(ppName);
    			}
    			else {
    				nonOrderedPostProcessorNames.add(ppName);
    			}
    		}
    
    		OrderComparator.sort(priorityOrderedPostProcessors);
    		//注册所有的BeanPostProcessor
    		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    
    		List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
    		for (String ppName : orderedPostProcessorNames) {
    			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    			orderedPostProcessors.add(pp);
    			if (pp instanceof MergedBeanDefinitionPostProcessor) {
    				internalPostProcessors.add(pp);
    			}
    		}
    		OrderComparator.sort(orderedPostProcessors);
    		registerBeanPostProcessors(beanFactory, orderedPostProcessors);
    
    		List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
    		for (String ppName : nonOrderedPostProcessorNames) {
    			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    			nonOrderedPostProcessors.add(pp);
    			if (pp instanceof MergedBeanDefinitionPostProcessor) {
    				internalPostProcessors.add(pp);
    			}
    		}
    		registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    
    		OrderComparator.sort(internalPostProcessors);
    		registerBeanPostProcessors(beanFactory, internalPostProcessors);
    
    		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector());
    	}

//在容器中添加BeanPostProcessor
    private void registerBeanPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
    
    		for (BeanPostProcessor postProcessor : postProcessors) {
    			beanFactory.addBeanPostProcessor(postProcessor);
    		}
    	}

#### 2、执行所有的BeanPostProcessor ####

在Spring容器在初始化Bean前后都会执行所有的BeanPostProcessor的实现类提供的方法。

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
    			throws BeansException {
    
    		Object result = existingBean;
    		//getBeanPostProcessors()获取所有的BeanPostProcessor的实现类
    		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
    			//执行BeanPostProcessor实现类的方法
    			result = beanProcessor.postProcessAfterInitialization(result, beanName);
    			if (result == null) {
    				return result;
    			}
    		}
    		return result;
    	}

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