后置bean工厂处理器 BeanFactoryPostProcessor 理解

spring初始化bean时对外暴露的扩展点有很多，比如BeanPostProcessor和BeanFactoryPostProcessor，它在spring容器加载了bean的定义文件之后，在bean实例化之前执行的。也就是说，Spring允许BeanFactoryPostProcessor在容器创建bean之前读取bean配置元数据，并可进行修改。例如增加bean的属性和值，重新设置bean是否作为自动装配的侯选者，重设bean的依赖项等等。

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 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
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 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;

/**
 * Allows for custom（定制的） modification of an application context's bean definitions,
 * adapting the bean property（属性） values of the context's underlying（底层） bean factory.
 *允许对应用上下文中bean定义做定制的修改，来适应bean的合适的上下文的底层bean工厂。
 * 
Application contexts can auto-detect BeanFactoryPostProcessor beans in
 * their bean definitions and apply them before any other beans get created.
 *应用上下文可以自动检测到BeanFactoryPostProcessor 的beans在它们的bean定义中并且会将在任何其他bean创建之前应用它（BeanFactoryPostProcessor ）。
 * 
Useful for custom config files targeted at system administrators that
 * override bean properties configured in the application context.
 *
 * 
See PropertyResourceConfigurer and its concrete implementations
 * for out-of-the-box solutions that address such configuration needs.
 *
 * 
A BeanFactoryPostProcessor may interact（相互作用） with and modify bean
 * definitions, but never bean instances. Doing so may cause premature（过早） bean
 * instantiation, violating（违反） the container and causing unintended（意外的） side-effects.
 * If bean instance interaction is required, consider implementing
 * {@link BeanPostProcessor} instead.
 *
 * @author Juergen Hoeller
 * @since 06.07.2003
 * @see BeanPostProcessor
 * @see PropertyResourceConfigurer
 */
public interface BeanFactoryPostProcessor {

	/**
	 * Modify the application context's internal bean factory after its standard
	 * initialization. All bean definitions will have been loaded, but no beans
	 * will have been instantiated yet. This allows for overriding or adding
	 * properties even to eager-initializing beans.
	 * @param beanFactory the bean factory used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
     //在bean标准初始化后，修改应用上下文的内部bean工厂。所有的bean定义都将被加载到这里。但是直到此时no beans已经完成初始化。这个方法允许overriding或者添加properties甚至紧急初始化beans。
     //这个方法的参数是ConfigurableListableBeanFactory ,它可以获取bean工厂，而工厂是可以根据bean的name或者class获取指定的bean的；
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}