org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator
Spring提供了很多擴充套件介面,BeanPostProcessor介面和InstantiationAwareBeanPostProcessor介面就是其中兩個。
BeanPostProcessor
BeanPostProcessor介面作用是:如果我們需要在Spring容器完成Bean的例項化、配置和其他的初始化前後新增一些自己的邏輯處理,我們就可以定義一個或者多個BeanPostProcessor介面的實現,然後註冊到容器中。
Spring中Bean的例項化過程圖示:
由上圖可以看到,Spring中的BeanPostProcessor在例項化過程處於的位置,BeanPostProcessor介面有兩個方法需要實現:postProcessBeforeInitialization和postProcessAfterInitialization,
- import org.springframework.beans.factory.config.BeanPostProcessor;
- publicclass MyBeanPostProcessor implements BeanPostProcessor {
- public MyBeanPostProcessor() {
- super();
- System.out.println("這是BeanPostProcessor實現類構造器!!");
- }
- @Override
- public
- throws BeansException {
- System.out.println("bean處理器:bean建立之後..");
- return bean;
- }
- @Override
- public Object postProcessBeforeInitialization(Object bean, String arg1)
- throws BeansException {
- System.out.println("bean處理器:bean建立之前..");
- return bean;
- }
- }
BeanPostProcessor介面定義如下:
Java程式碼- publicinterface 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;
- }
由方法名字也可以看出,前者在例項化及依賴注入完成後、在任何初始化程式碼(比如配置檔案中的init-method)呼叫之前呼叫;後者在初始化程式碼呼叫之後呼叫。
注意:
1、介面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會自動檢測在配置檔案中實現了BeanPostProcessor介面的所有bean,並把它們註冊為後置處理器,然後在容器建立bean的適當時候呼叫它,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程式碼顯式地去註冊,在IoC容器繼承體系中的ConfigurableBeanFactory介面中定義了註冊方法:
Java程式碼- /**
- * 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標記為延遲初始化。因為如果這樣做,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標記為'lazy-init="false"'。
InstantiationAwareBeanPostProcessor
InstantiationAwareBeanPostProcessor是BeanPostProcessor的子介面,可以在Bean生命週期的另外兩個時期提供擴充套件的回撥介面,即例項化Bean之前(呼叫postProcessBeforeInstantiation方法)和例項化Bean之後(呼叫postProcessAfterInstantiation方法),該介面定義如下:Java程式碼
- package org.springframework.beans.factory.config;
- import java.beans.PropertyDescriptor;
- import org.springframework.beans.BeansException;
- import org.springframework.beans.PropertyValues;
- publicinterface 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;
- }