Spring中BeanPostProcessor

Spring提供了很多擴展接口，BeanPostProcessor接口和InstantiationAwareBeanPostProcessor接口就是其中兩個。

 

BeanPostProcessor

BeanPostProcessor接口作用是：如果我們需要在Spring容器完成Bean的實例化、配置和其他的初始化前後添加一些自己的邏輯處理，我們就可以定義一個或者多個BeanPostProcessor接口的實現，然後註冊到容器中。

Spring中Bean的實例化過程圖示：

由上圖可以看到，Spring中的BeanPostProcessor在實例化過程處於的位置，BeanPostProcessor接口有兩個方法需要實現：postProcessBeforeInitialization和postProcessAfterInitialization，

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

public class MyBeanPostProcessor implements BeanPostProcessor {

     public MyBeanPostProcessor() {
        super();
        System.out.println("這是BeanPostProcessor實現類構造器！！");
     }

     @Override
     public Object postProcessAfterInitialization(Object bean, String arg1)
             throws BeansException {
         System.out.println("bean處理器：bean創建之後..");
         return bean;
     }

     @Override
     public Object postProcessBeforeInitialization(Object bean, String arg1)
             throws BeansException {
         System.out.println("bean處理器：bean創建之前..");

         return bean;
     }
 }

import org.springframework.beans.factory.config.BeanPostProcessor;
 
public class MyBeanPostProcessor implements BeanPostProcessor {
 
     public MyBeanPostProcessor() {
        super();
        System.out.println("這是BeanPostProcessor實現類構造器！！");        
     }
 
     @Override
     public Object postProcessAfterInitialization(Object bean, String arg1)
             throws BeansException {
         System.out.println("bean處理器：bean創建之後..");
         return bean;
     }
 
     @Override
     public Object postProcessBeforeInitialization(Object bean, String arg1)
             throws BeansException {
         System.out.println("bean處理器：bean創建之前..");
	 
         return bean;
     }
 }

 

BeanPostProcessor接口定義如下：

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，在調用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.
     */
//實例化、依賴注入、初始化完畢時執行
    Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

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，在調用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.      
	 */
//實例化、依賴注入、初始化完畢時執行
	Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

 

 

由方法名字也可以看出，前者在實例化及依賴注入完成後、在任何初始化代碼（比如配置文件中的init-method）調用之前調用；後者在初始化代碼調用之後調用。

注意：

1、接口中的兩個方法都要將傳入的bean返回，而不能返回null，如果返回的是null那麼我們通過getBean方法將得不到目標。

 

2、BeanFactory和ApplicationContext對待bean後置處理器稍有不同。ApplicationContext會自動檢測在配置文件中實現了BeanPostProcessor接口的所有bean，並把它們註冊爲後置處理器，然後在容器創建bean的適當時候調用它，因此部署一個後置處理器同部署其他的bean並沒有什麼區別。而使用BeanFactory實現的時候，bean 後置處理器必須通過代碼顯式地去註冊，在IoC容器繼承體系中的ConfigurableBeanFactory接口中定義了註冊方法：

 

/**
 * 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);

/** 
 * 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); 

 

 

另外，不要將BeanPostProcessor標記爲延遲初始化。因爲如果這樣做，Spring容器將不會註冊它們，自定義邏輯也就無法得到應用。假如你在<beans />元素的定義中使用了'default-lazy-init'屬性，請確信你的各個BeanPostProcessor標記爲'lazy-init="false"'。

 

InstantiationAwareBeanPostProcessor

InstantiationAwareBeanPostProcessor是BeanPostProcessor的子接口，可以在Bean生命週期的另外兩個時期提供擴展的回調接口，即實例化Bean之前（調用postProcessBeforeInstantiation方法）和實例化Bean之後（調用postProcessAfterInstantiation方法），該接口定義如下：

package org.springframework.beans.factory.config;

import java.beans.PropertyDescriptor;

import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {

    Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;

    boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;

    PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)
            throws BeansException;

}

package org.springframework.beans.factory.config;  
  
import java.beans.PropertyDescriptor;  
  
import org.springframework.beans.BeansException;  
import org.springframework.beans.PropertyValues;  
  
public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {  
  
    Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;  
  
    boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;  
  
    PropertyValues postProcessPropertyValues(  
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)  
            throws BeansException;  
  
}

 其使用方法與上面介紹的BeanPostProcessor接口類似，只時回調時機不同。

 

如果是使用ApplicationContext來生成並管理Bean的話則稍有不同，使用ApplicationContext來生成及管理Bean實例的話，在執行BeanFactoryAware的setBeanFactory()階段後，若Bean類上有實現org.springframework.context.ApplicationContextAware接口，則執行其setApplicationContext()方法，接着才執行BeanPostProcessors的ProcessBeforeInitialization()及之後的流程。