BeanPostProcessor定義爲在創建組件時,執行組件的初始化方法(InitializingBean的實現類或者init-method指定的初始化方法)的前後做一些事情,可以是對組件的一些檢查,或者對組件進行包裝,或者創建組件的代理;
BeanPostProcessor接口定義如下:
package org.springframework.beans.factory.config;
import org.springframework.beans.BeansException;
public interface BeanPostProcessor {
/**
在所有初始化之前被調用,返回的是原來的組件或者是組件的包裝類
*/
Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
/**
在所有初始化之後被調用,返回的是原來的組件或者是組件的包裝類
*/
Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}
BeanPostProcessor具體是在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(String, Object, RootBeanDefinition)中被調用,具體流程如下:
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
invokeAwareMethods(beanName, bean);
return null;
}
}, getAccessControlContext());
}
else {
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
if (mbd == null || !mbd.isSynthetic()) {
//在組件執行初始化方法之前,遍歷所有BeanPostProcessor,並調用postProcessBeforeInitialization方法
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//調用組件的初始化方法
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
if (mbd == null || !mbd.isSynthetic()) {
//組件執行所有初始化方法之後,遍歷所有BeanPostProcessor,並調用postProcessAfterInitialization方法
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
return wrappedBean;
}