Spring源码学习--BeanPostProcessor-蒲公英云

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

<bean class="com.spring.test.di.MyBeanPostProcessor"/>

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;
    }