资深小白谈spring（十六）：registerBeanPostProcessors

我会带着你远行 2022-09-12 09:00 132阅读 0赞

### 资深小白谈spring（十六）：registerBeanPostProcessors ###

1、registerBeanPostProcessors调用了PostProcessorRegistrationDelegate的registerBeanPostProcessors方法，该方法做的事情就三样：创建BeanPostProcessors、排序以及注册。  
![在这里插入图片描述][cdf0ed9d31814abda1899e99486ac656.png]

public static void registerBeanPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
        
    
    		//获取所有BeanPostProcessor的beanName
    		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    
    		// Register BeanPostProcessorChecker that logs an info message when
    		// a bean is created during BeanPostProcessor instantiation, i.e. when
    		// a bean is not eligible for getting processed by all BeanPostProcessors.
    		int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    		beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    
    
    		List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    		List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
    		List<String> orderedPostProcessorNames = new ArrayList<>();
    		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    		for (String ppName : postProcessorNames) {
        
    			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
        
    				BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    				priorityOrderedPostProcessors.add(pp);
    				if (pp instanceof MergedBeanDefinitionPostProcessor) {
        
    					internalPostProcessors.add(pp);
    				}
    			}
    			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
        
    				orderedPostProcessorNames.add(ppName);
    			}
    			else {
        
    				nonOrderedPostProcessorNames.add(ppName);
    			}
    		}
    
    		// 与BeanFactoryPostProcessor一样先对实现了PriorityOrdered接口进行排序
    		// 然后再对实现了Order接口进行排序
    		// 不一样的就是BeanFactoryPostProcessor是直接调用postProcessBeanFactory方法
    		// 而这里只是对beanPostProcessor进行注册
    		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    		registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    
    		List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
    		for (String ppName : orderedPostProcessorNames) {
        
    			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    			orderedPostProcessors.add(pp);
    			if (pp instanceof MergedBeanDefinitionPostProcessor) {
        
    				internalPostProcessors.add(pp);
    			}
    		}
    		sortPostProcessors(orderedPostProcessors, beanFactory);
    		registerBeanPostProcessors(beanFactory, orderedPostProcessors);
    
    		List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
    		for (String ppName : nonOrderedPostProcessorNames) {
        
    			BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    			nonOrderedPostProcessors.add(pp);
    			if (pp instanceof MergedBeanDefinitionPostProcessor) {
        
    				internalPostProcessors.add(pp);
    			}
    		}
    		registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    
    		sortPostProcessors(internalPostProcessors, beanFactory);
    		registerBeanPostProcessors(beanFactory, internalPostProcessors);
    
    		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    	}

2、排序的原理在上一节中已经详细地分析过了，现在主要看注册过程。注册很简单，就是调用beanFactory的addBeanPostProcessor进行注册。

private static void registerBeanPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
        
    
    		for (BeanPostProcessor postProcessor : postProcessors) {
        
    			beanFactory.addBeanPostProcessor(postProcessor);
    		}
    	}

3、把beanPostProcessors收集到beanFactory的beanPostProcessors容器中，完成注册过程。

private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
    
    	public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
        
    		Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
    		// Remove from old position, if any
    		this.beanPostProcessors.remove(beanPostProcessor);
    		// Track whether it is instantiation/destruction aware
    		if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
        
    			this.hasInstantiationAwareBeanPostProcessors = true;
    		}
    		if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
        
    			this.hasDestructionAwareBeanPostProcessors = true;
    		}
    		// 关键代码，这里把beanPostProcessor收集到了beanPostProcessors容器
    		this.beanPostProcessors.add(beanPostProcessor);
    	}

4、现在我们对B类进行修改，实现BeanPostProcessor接口：  
![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBASmFua2VEZW5n_size_20_color_FFFFFF_t_70_g_se_x_16]  
5、运行结果如下，通过运行结果可以看到B优先被创建，然后在创建A的时候先执行postProcessBeforeInitialization方法再执行postProcessAfterInitialization方法。  
![在这里插入图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBASmFua2VEZW5n_size_20_color_FFFFFF_t_70_g_se_x_16 1]6、结语：BeanPostProcessor是spring给我提供的一个创建Bean的生命周期，在这个周期里面我们可以对Bean进行自定义的修改。

*  上一篇：[资深小白谈spring（十五）：invokeBeanFactoryPostProcessors][spring_invokeBeanFactoryPostProcessors]
 *  下一篇：[资深小白谈spring（十七）：BeanDefinition的合并原理][spring_BeanDefinition]

[cdf0ed9d31814abda1899e99486ac656.png]: /images/20220828/989e3ee386da431cb38f34dd4f76d310.png
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBASmFua2VEZW5n_size_20_color_FFFFFF_t_70_g_se_x_16]: /images/20220828/37ffa7dc4cdd4fc7b0be3a777bec4537.png
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBASmFua2VEZW5n_size_20_color_FFFFFF_t_70_g_se_x_16 1]: /images/20220828/2340f39de4424546857a5349e9755370.png
[spring_invokeBeanFactoryPostProcessors]: https://blog.csdn.net/JankeDeng/article/details/120408530?spm=1001.2014.3001.5501
[spring_BeanDefinition]: https://blog.csdn.net/JankeDeng/article/details/120449562?spm=1001.2014.3001.5502