一、BeanPostProcessor這個是spring容器的拓展之一，是用於獲取bean的時候處理對應的物件；

　　二、常用場景，在獲取bean的時候，重新初始化bean的屬性等。

　　三、實現方式（加入容器後，呼叫其他bean的時候，通過BeanPostProcessor來進行處理）

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

public class BeanPostProcessorTest implements
 
 BeanPostProcessor{

    /**
     * 在bean載入之前處理
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("before");
        
 
return bean;
    }

    /**
     * 在bean載入之後處理
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("after");
        
 
return bean;
    }
}

　　四、原始碼部分

　　1）容器中的註冊部分為refresh()中的registerBeanPostProcessors()方法，注意這裡只是註冊，實際呼叫在getBean的時候

this.registerBeanPostProcessors(beanFactory);

　　2）registerBeanPostProcessors

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        //在容器中獲取獲取實現BeanPostProcessor的bean
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new AbstractApplicationContext.BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
        //宣告不同BeanPostProcessor型別(priorityOrdered,internal,ordered,non 按照順序，和優先順序執行)
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList();
        List<BeanPostProcessor> internalPostProcessors = new ArrayList();
        List<String> orderedPostProcessorNames = new ArrayList();
        List<String> nonOrderedPostProcessorNames = new ArrayList();
        String[] var11 = postProcessorNames;
        int var10 = postProcessorNames.length;

        BeanPostProcessor pp;
        for(int var9 = 0; var9 < var10; ++var9) {
            String ppName = var11[var9];
            //判斷時什麼型別
            if (this.isTypeMatch(ppName, PriorityOrdered.class)) {
                pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                //此介面存在postProcessMergedBeanDefinition的介面
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            } else if (this.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            } else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }
        //排序
        OrderComparator.sort(priorityOrderedPostProcessors);
        //新增到beanPostProcessors（private final List<BeanPostProcessor> beanPostProcessors = new ArrayList();）
        this.registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList();
        Iterator var16 = orderedPostProcessorNames.iterator();

        while(var16.hasNext()) {
            String ppName = (String)var16.next();
            BeanPostProcessor pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }

        //排序
        OrderComparator.sort(orderedPostProcessors);
        this.registerBeanPostProcessors(beanFactory, orderedPostProcessors);
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList();
        Iterator var19 = nonOrderedPostProcessorNames.iterator();

        while(var19.hasNext()) {
            String ppName = (String)var19.next();
            pp = (BeanPostProcessor)beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }

        this.registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
        OrderComparator.sort(internalPostProcessors);
        this.registerBeanPostProcessors(beanFactory, internalPostProcessors);
        beanFactory.addBeanPostProcessor(new AbstractApplicationContext.ApplicationListenerDetector((AbstractApplicationContext.ApplicationListenerDetector)null));
    }

    private void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
        Iterator var4 = postProcessors.iterator();

        while(var4.hasNext()) {
            BeanPostProcessor postProcessor = (BeanPostProcessor)var4.next();
            //新增到beanPostProcessors（private final List<BeanPostProcessor> beanPostProcessors = new ArrayList();）
            beanFactory.addBeanPostProcessor(postProcessor);
        }
    }

　　3）addBeanPostProcessor（DefaultListableBeanFactory，中快取的List<String> beanDefinitionNames = new ArrayList()）

　　public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
        Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
        this.beanPostProcessors.remove(beanPostProcessor);
        //新增到beanPostProcessors中
        this.beanPostProcessors.add(beanPostProcessor);
        if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
            this.hasInstantiationAwareBeanPostProcessors = true;
        }

        if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
            this.hasDestructionAwareBeanPostProcessors = true;
        }
    }

　　五、呼叫方式（在個getBean的時候回自動按照優先順序呼叫BeanPostProcessor）

　　具體實現見：spring原始碼-bean之載入-2的四、原始碼實現3).d createBean部分