BeanPostProcessor介面作用：

     如果我們想在Spring容器中完成bean例項化、配置以及其他初始化方法前後要新增一些自己邏輯處理。我們需要定義一個或多個BeanPostProcessor介面實現類，然後註冊到Spring IoC容器中。

package com.test.spring;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
/**
 * bean後置處理器
 * @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例項ID為narCodeService
            return bean;
        }
        System.out.println("後置處理器處理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("後置處理器處理bean=【"+beanName+"】完畢!");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }

}

 

注意:介面中兩個方法不能返回null，如果返回null那麼在後續初始化方法將報空指標異常或者通過getBean()方法獲取不到bean例項物件 ，因為後置處理器從Spring IOC容器中取出bean例項物件沒有再次放回IOC容器中 。

將Spring的後置處理器PostProcessor配置到Spring配置檔案中

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">

    <!-- 定義一個bean -->
     <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">
     </bean>
    <bean id="beanLifecycle" class="com.test.spring.BeanLifecycle" init-method="init" destroy-method="close">
        <property name="name" value="張三"></property>
        <property name="sex" value="男"></property>
    </bean>

    <!-- Spring後置處理器 -->
    <bean id="postProcessor" class="com.test.spring.PostProcessor"/>
</beans>
 

 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.    
     */  
    //例項化、依賴注入完畢，在呼叫顯示的初始化之前完成一些定製的初始化任務  
    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.       
     */  
    //例項化、依賴注入、初始化完畢時執行  
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;  
  
}
 

由API可以看出:
1：後置處理器的postProcessorBeforeInitailization方法是在bean例項化，依賴注入之後及自定義初始化方法(例如：配置檔案中bean標籤新增init-method屬性指定Java類中初始化方法、
@PostConstruct註解指定初始化方法，Java類實現InitailztingBean介面)之前呼叫
2：後置處理器的postProcessorAfterInitailization方法是在bean例項化、依賴注入及自定義初始化方法之後呼叫

注意：
   1.BeanFactory和ApplicationContext兩個容器對待bean的後置處理器稍微有些不同。ApplicationContext容器會自動檢測Spring配置檔案中那些bean所對應的Java類實現了BeanPostProcessor介面，並自動把它們註冊為後置處理器。在建立bean過程中呼叫它們，所以部署一個後置處理器跟普通的bean沒有什麼太大區別。

      2.BeanFactory容器註冊bean後置處理器時必須通過程式碼顯示的註冊，在IoC容器繼承體系中的ConfigurableBeanFactory介面中定義了註冊方法

/**  
     * 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如何呼叫多個BeanPostProcessor實現類：

    我們可以在Spring配置檔案中新增多個BeanPostProcessor(後置處理器)介面實現類，在預設情況下Spring容器會根據後置處理器的定義順序來依次呼叫。

Spring配置檔案：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
    <!-- bean定義 -->    
    <bean id="narCodeService" class="com.test.service.impl.NarCodeServiceImpl">
    </bean>
    <bean id="postProcessor" class="com.test.spring.PostProcessor"/>
    <bean id="postProcessorB" class="com.test.spring.PostProcessorB"/>
</beans>

BeanPostProcessor實現類：

package com.test.spring;

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

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException {
        System.out.println("後置處理器處理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 {
        System.out.println("後置處理器處理bean=【"+beanName+"】完畢!");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }
}
----------------------------------------------------------------------------------------------------------------------------------------
package com.test.spring;

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

public class PostProcessorB implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException {
        System.out.println("後置處理器開始呼叫了");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException {
        System.out.println("後置處理器呼叫結束了");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }
}

測試：

package com.test.spring;

import org.junit.Before;
import org.junit.Test;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class T {
    AbstractApplicationContext applicationcontext=null;
    @Before
    public void before() {
        System.out.println("》》》Spring ApplicationContext容器開始初始化了......");
        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});
        System.out.println("》》》Spring ApplicationContext容器初始化完畢了......");
    }
    @Test
    public void  test() {
        applicationcontext.registerShutdownHook();   
    }
}

測試結果：

》》》Spring ApplicationContext容器開始初始化了......
2017-03-19 10:50:29  INFO:ClassPathXmlApplicationContext-Refreshing org[email protected]18c92ff9: startup date [Sun Mar 19 10:50:29 CST 2017]; root of context hierarchy
2017-03-19 10:50:29  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
後置處理器處理bean=【narCodeService】開始
後置處理器開始呼叫了
後置處理器處理bean=【narCodeService】完畢!
後置處理器呼叫結束了
》》》Spring ApplicationContext容器初始化完畢了......
2017-03-19 10:50:34  INFO:ClassPathXmlApplicationContext-Closing org[email protected]18c92ff9: startup date [Sun Mar 19 10:50:29 CST 2017]; root of context hierarchy

   在Spring機制中可以指定後置處理器呼叫順序，通過讓BeanPostProcessor介面實現類實現Ordered介面getOrder方法，該方法返回一整數，預設值為 0，優先順序最高，值越大優先順序越低

例如：

package com.test.spring;

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

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

    @Override
    public int getOrder() {
        return 1;
    }
}
----------------------------------------------------------------------------
package com.test.spring;

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

public class PostProcessorB implements BeanPostProcessor,Ordered {

    @Override
    public Object postProcessBeforeInitialization(Object bean,
            String beanName) throws BeansException {
        System.out.println("後置處理器開始呼叫了");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean,
            String beanName) throws BeansException {
        System.out.println("後置處理器呼叫結束了");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return bean;
    }

    @Override
    public int getOrder() {
        return 0;
    }
}

測試結果：

》》》Spring ApplicationContext容器開始初始化了......
2017-03-19 11:04:10  INFO:ClassPathXmlApplicationContext-Refreshing org[email protected]18c92ff9: startup date [Sun Mar 19 11:04:10 CST 2017]; root of context hierarchy
2017-03-19 11:04:10  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
後置處理器開始呼叫了
後置處理器處理bean=【narCodeService】開始
後置處理器呼叫結束了
後置處理器處理bean=【narCodeService】完畢!
》》》Spring ApplicationContext容器初始化完畢了......
2017-03-19 11:04:14  INFO:ClassPathXmlApplicationContext-Closing org[email protected]18c92ff9: startup date [Sun Mar 19 11:04:10 CST 2017]; root of context hierarchy