Spring - BeanFactoryPostProcessor 扩展接口

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Spring Boot - 扩展接口一览


org.springframework.beans.factory.config.BeanFactoryPostProcessor

这个接口是beanFactory的扩展接口,调用时机在spring在读取beanDefinition信息之后,实例化bean之前。

在这个时机,用户可以通过实现这个扩展接口来自行处理一些东西,比如修改已经注册的beanDefinition的元信息


package org.springframework.beans.factory.config;

import org.springframework.beans.BeansException;

/**
 * Factory hook that allows for custom modification of an application context's
 * bean definitions, adapting the bean property values of the context's underlying
 * bean factory.
 *
 * <p>Useful for custom config files targeted at system administrators that
 * override bean properties configured in the application context. See
 * @link PropertyResourceConfigurer and its concrete implementations for
 * out-of-the-box solutions that address such configuration needs.
 *
 * <p>A @code BeanFactoryPostProcessor may interact with and modify bean
 * definitions, but never bean instances. Doing so may cause premature bean
 * instantiation, violating the container and causing unintended side-effects.
 * If bean instance interaction is required, consider implementing
 * @link BeanPostProcessor instead.
 *
 * <h3>Registration</h3>
 * <p>An @code ApplicationContext auto-detects @code BeanFactoryPostProcessor
 * beans in its bean definitions and applies them before any other beans get created.
 * A @code BeanFactoryPostProcessor may also be registered programmatically
 * with a @code ConfigurableApplicationContext.
 *
 * <h3>Ordering</h3>
 * <p>@code BeanFactoryPostProcessor beans that are autodetected in an
 * @code ApplicationContext will be ordered according to
 * @link org.springframework.core.PriorityOrdered and
 * @link org.springframework.core.Ordered semantics. In contrast,
 * @code BeanFactoryPostProcessor beans that are registered programmatically
 * with a @code ConfigurableApplicationContext will be applied in the order of
 * registration; any ordering semantics expressed through implementing the
 * @code PriorityOrdered or @code Ordered interface will be ignored for
 * programmatically registered post-processors. Furthermore, the
 * @link org.springframework.core.annotation.Order @Order annotation is not
 * taken into account for @code BeanFactoryPostProcessor beans.
 *
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 06.07.2003
 * @see BeanPostProcessor
 * @see PropertyResourceConfigurer
 */
@FunctionalInterface
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
	 */
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;



spring容器初始化时,从资源中读取到bean的相关定义后,保存在beanFactory的成员变量中(DefaultListableBeanFactory#beanDefinitionMap)

private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);

实例化bean的操作就是依据这些BeanDefinition来做的。

在实例化之前,spring允许我们通过自定义扩展来改变bean的定义,定义一旦变了,后面的实例也就变了,而beanFactory后置处理器BeanFactoryPostProcessor就是用来改变bean定义的。


源码探究

AbstractApplicationContext#refresh 继续走起

继续

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

主要功能是: 找出所有beanFactory后置处理器,并且调用这些处理器来改变bean的定义

继续 org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors

	/**
	 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
	 * respecting explicit order if given.
	 * <p>Must be called before singleton instantiation.
	 */
	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) 
		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

		.......

我们重点关注PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

代码比较长,我们逐段看一下

1 是否实现BeanDefinitionRegistryPostProcessor 接口,分别写入集合

	for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) 
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) 
					BeanDefinitionRegistryPostProcessor registryProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryProcessor.postProcessBeanDefinitionRegistry(registry);
					registryProcessors.add(registryProcessor);
				
				else 
					regularPostProcessors.add(postProcessor);
				
			

遍历入参 beanFactoryPostProcessors , 是否实现了BeanDefinitionRegistryPostProcessor,分别放入两个集合:registryProcessors和regularPostProcessors;


2 处理实现了的PriorityOrdered和 BeanDefinitionRegistryPostProcessors 的 bean

// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
			String[] postProcessorNames =
					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) 
				if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) 
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					processedBeans.add(ppName);
				
			
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
			currentRegistryProcessors.clear();

找出所有实现了BeanDefinitionRegistryPostProcessor接口和PriorityOrdered接口的bean,放入registryProcessors集合,根据PriorityOrdered接口来排序,然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行;


3. 处理实现了的Ordered和BeanDefinitionRegistryPostProcessors 的 bean

// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) 
				if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) 
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					processedBeans.add(ppName);
				
			
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
			currentRegistryProcessors.clear();

找出所有实现了BeanDefinitionRegistryPostProcessor接口和Ordered接口的bean,放入registryProcessors集合,根据Ordered接口来排序,然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行;


4 处理其他实现了BeanDefinitionRegistryPostProcessor的bean

	// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
			boolean reiterate = true;
			while (reiterate) 
				reiterate = false;
				postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
				for (String ppName : postProcessorNames) 
					if (!processedBeans.contains(ppName)) 
						currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
						processedBeans.add(ppName);
						reiterate = true;
					
				
				sortPostProcessors(currentRegistryProcessors, beanFactory);
				registryProcessors.addAll(currentRegistryProcessors);
				invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
				currentRegistryProcessors.clear();
			

对于那些实现了BeanDefinitionRegistryPostProcessor接口,但是没有实现PriorityOrdered和Ordered的bean也被找出来,然后这些bean会被invokeBeanDefinitionRegistryPostProcessors方法执行


5 invokeBeanFactoryPostProcessors

// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);

6 除了试下BeanDefinitionRegistryPostProcessor之外的其他 实现了BeanFactoryPostProcessor接口的bean 分类

	// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

		// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
		// Ordered, and the rest.
		List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
		List<String> orderedPostProcessorNames = new ArrayList<>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
		for (String ppName : postProcessorNames) 
			if (processedBeans.contains(ppName)) 
				// skip - already processed in first phase above
			
			else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) 
				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
			
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) 
				orderedPostProcessorNames.add(ppName);
			
			else 
				nonOrderedPostProcessorNames.add(ppName);
			
		

找出实现了BeanFactoryPostProcessor接口的bean,注意这里已将前面实现了BeanDefinitionRegistryPostProcessor接口的bean给剔除了

if (processedBeans.contains(ppName)) 
	// skip - already processed in first phase above

将这些bean分为三类:

  • 实现了PriorityOrdered接口的放入priorityOrderedPostProcessors,
  • 实现了Ordered接口的放入orderedPostProcessorNames,
  • 其他的放入nonOrderedPostProcessorNames,这段代码是关键,自定义的实现BeanFactoryPostProcessor接口的bean就会在此处被查找出来。

7 处理 PriorityOrdered ,invokeBeanDefinitionRegistryPostProcessors

// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

8 处理 Ordered ,invokeBeanDefinitionRegistryPostProcessors

// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
		for (String postProcessorName : orderedPostProcessorNames) 
			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		
		sortPostProcessors(orderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

9 处理剩下的 ,invokeBeanDefinitionRegistryPostProcessors

// Finally, invoke all other BeanFactoryPostProcessors.
		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
		for (String postProcessorName : nonOrderedPostProcessorNames) 
			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);


10 invokeBeanDefinitionRegistryPostProcessors & invokeBeanFactoryPostProcessors 分析

从上面的分析可以发现,所有实现了BeanFactoryPostProcessor接口的bean,都被作为入参,然后调用了invokeBeanDefinitionRegistryPostProcessors或者invokeBeanFactoryPostProcessors方法去处理

	/**
	 * Invoke the given BeanDefinitionRegistryPostProcessor beans.
	 */
	private static void invokeBeanDefinitionRegistryPostProcessors(
			Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) 

		for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) 
			StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
					.tag("postProcessor", postProcessor::toString);
			postProcessor.postProcessBeanDefinitionRegistry(registry);
			postProcessBeanDefRegistry.end();
		
	
	/**
	 * Invoke the given BeanFactoryPostProcessor beans.
	 */
	private static void invokeBeanFactoryPostProcessors(
			Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) 

		for (BeanFactoryPostProcessor postProcessor : postProcessors) 
			StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process")
					.tag("postProcessor", postProcessor::toString);
			postProcessor.postProcessBeanFactory(beanFactory);
			postProcessBeanFactory.end();
		
	

对每个BeanFactoryPostProcessor接口的实现类,都调用了其接口方法。
不同的是 对于实现了BeanDefinitionRegistryPostProcessor接口的bean,调用其postProcessBeanDefinitionRegistry方法的时候,入参是BeanDefinitionRegistry,而非BeanFactory,因此,实现了BeanDefinitionRegistryPostProcessor接口的bean,其postProcessBeanDefinitionRegistry在被调用时,可以通过入参BeanDefinitionRegistry来做更多和bean的定义有关的操作,例如注册bean等等、


BeanFactoryPostProcessor的处理流程

小结一下:

  • ApplicationContext扩展类可以调用AbstractApplicationContext.addBeanFactoryPostProcessor方法,将自定义的BeanFactoryPostProcessor实现类保存到ApplicationContext中;
  • spring容器初始化时,上一步中被加入到ApplicationContext的bean会被优先调用其postProcessBeanFactory方法;
  • 自定义的BeanFactoryPostProcessor接口实现类,也会被找出来,然后调用其postProcessBeanFactory方法;
  • postProcessBeanFactory方法被调用时,beanFactory会被作为参数传入,自定义类中可以使用该参数来处理bean的定义,达到业务需求;
  • 此时的spring容器还没有开始实例化bean,因此自定义的BeanFactoryPostProcessor实现类不要做与bean实例有关的操作,而是做一些与bean定义有关的操作,例如修改某些字段的值,这样后面实例化的bean的就会有相应的改变;

扩展方式

package com.artisan.bootspringextend.testextends;

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.context.annotation.Configuration;

/**
 * @author 小工匠
 * @version 1.0 
 * @date 2022/11/27 16:58
 * @mark: show me the code , change the world
 */

@Slf4j
@Configuration
public class ExtendBeanFactoryPostProcessor implements BeanFactoryPostProcessor 
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException 
        log.info("----->postProcessBeanFactory called ");
    

    

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