BeanPostProcessor接口作用：

如果我們想在Spring容器中完成bean實例化、配置以及其他初始化方法前后要添加一些自己邏輯處理。我們需要定義一個或多個BeanPostProcessor接口實現(xiàn)類，然后注冊到Spring IoC容器中。

package com.test.spring;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
/**
 * bean后置處理器
 * @author zss
 *
 */
public class PostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException {
        if ("narCodeService".equals(beanName)) {//過濾掉bean實例ID為narCodeService
            return bean;
        }
        System.out.println("后置處理器處理bean=【"+beanName+"】開始");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException {
        if ("narCodeService".equals(beanName)) {
            return bean;
        }
        System.out.println("后置處理器處理bean=【"+beanName+"】完畢!");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }

}

注意:接口中兩個方法不能返回null，如果返回null那么在后續(xù)初始化方法將報空指針異?；蛘咄ㄟ^getBean()方法獲取不到bena實例對象
     因為后置處理器從Spring IoC容器中取出bean實例對象沒有再次放回IoC容器中

## BeanPostProcessor API：

public interface BeanPostProcessor {  
  
    /** 
     * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean 
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet} 
     * or a custom init-method). The bean will already be populated with property values.    
     */  
    //實例化、依賴注入完畢，在調(diào)用顯示的初始化之前完成一些定制的初始化任務  
    Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;  
  
      
    /** 
     * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean 
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}   
     * or a custom init-method). The bean will already be populated with property values.       
     */  
    //實例化、依賴注入、初始化完畢時執(zhí)行  
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;  
  
}

由API可以看出:
1：后置處理器的postProcessorBeforeInitailization方法是在bean實例化，依賴注入之后及自定義初始化方法(例如：配置文件中bean標簽添加init-method屬性指定Java類中初始化方法、
@PostConstruct注解指定初始化方法，Java類實現(xiàn)InitailztingBean接口)之前調(diào)用
2：后置處理器的postProcessorAfterInitailization方法是在bean實例化、依賴注入及自定義初始化方法之后調(diào)用

注意：
1.BeanFactory和ApplicationContext兩個容器對待bean的后置處理器稍微有些不同。ApplicationContext容器會自動檢測Spring配置文件中那些bean所對應的Java類實現(xiàn)了BeanPostProcessor
接口，并自動把它們注冊為后置處理器。在創(chuàng)建bean過程中調(diào)用它們，所以部署一個后置處理器跟普通的bean沒有什么太大區(qū)別。
2.BeanFactory容器注冊bean后置處理器時必須通過代碼顯示的注冊，在IoC容器繼承體系中的ConfigurableBeanFactory接口中定義了注冊方法

/**  
     * Add a new BeanPostProcessor that will get applied to beans created  
     * by this factory. To be invoked during factory configuration.  
     * <p>Note: Post-processors submitted here will be applied in the order of  
     * registration; any ordering semantics expressed through implementing the  
     * {@link org.springframework.core.Ordered} interface will be ignored. Note  
     * that autodetected post-processors (e.g. as beans in an ApplicationContext)  
     * will always be applied after programmatically registered ones.  
     * @param beanPostProcessor the post-processor to register  
     */    
    void addBeanPostProcessor(BeanPostProcessor beanPostProcessor);

Spring如何調(diào)用多個BeanPostProcessor實現(xiàn)類：

我們可以在Spring配置文件中添加多個BeanPostProcessor(后置處理器)接口實現(xiàn)類，在默認情況下Spring容器會根據(jù)后置處理器的定義順序來依次調(diào)用。
在Spring機制中可以指定后置處理器調(diào)用順序，通過讓BeanPostProcessor接口實現(xiàn)類實現(xiàn)Ordered接口getOrder方法，該方法返回一整數(shù)，默認值為 0，優(yōu)先級最高，值越大優(yōu)先級越低