Spring源码深度解析（十）——Spring内置后置处理器哪来的

偏执的太偏执、 2023-07-16 03:55 1阅读 0赞

今天在看源码的时候，有些后置处理器莫名其妙就加了进来，因此我就看看它是从哪来的？

Spring内部会加载的选项如下

/**
    	 * Register all relevant annotation post processors in the given registry.
    	 * @param registry the registry to operate on
    	 * @param source the configuration source element (already extracted)
    	 * that this registration was triggered from. May be {@code null}.
    	 * @return a Set of BeanDefinitionHolders, containing all bean definitions
    	 * that have actually been registered by this call
    	 */
    	public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
    			BeanDefinitionRegistry registry, @Nullable Object source) {
    
    		//得到DefaultListableBeanFactory工厂
    		DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
    		if (beanFactory != null) {
    			//判断有没有排序相关的注解
    			if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
    				//(1)AnnotationAwareOrderComparator主要解析@Priority和@Order等排序注解
    				beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
    			}
    			if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
    				//(2)提供处理延迟加载功能ContextAnnotationAutowireCandidateResolver
    				beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
    			}
    		}
    
    		//BeanDefinitionHolder是存的beanName，alias和BeanDefinition的一个对应关系的数据结构
    		Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
    
    		if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
    			//(3)internalConfigurationAnnotationProcessor，处理配置类
    			RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
    			def.setSource(source);
    			//间接调用BDR的registryBeanDefinition方法将这个BD注册进Map去
    			beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
    		}
    
    		// 注册AutowiredAnnotationProcessor
    		if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
    			//（4）internalAutowiredAnnotationProcessor  处理@Autowired
    			RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
    			def.setSource(source);
    			beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
    		}
    
    		// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
    		if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
    			// （5）internalCommonAnnotationProcessor   在bean实例化那块有用到
    			RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
    			def.setSource(source);
    			beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
    		}
    
    		// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
    		if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
    			// （6）internalPersistenceAnnotationProcessor  如果存在jpa支持就注册
    			RootBeanDefinition def = new RootBeanDefinition();
    			try {
    				def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
    						AnnotationConfigUtils.class.getClassLoader()));
    			}
    			catch (ClassNotFoundException ex) {
    				throw new IllegalStateException(
    						"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
    			}
    			def.setSource(source);
    			beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
    		}
    
    		if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
    			//（7）internalEventListenerProcessor   事件监听后置处理器
    			RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
    			def.setSource(source);
    			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
    		}
    
    		if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
    			//（8）internalEventListenerFactory  事件监听工厂
    			RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
    			def.setSource(source);
    			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
    		}
    
    		return beanDefs;
    	}

可以看到在单纯的Spring会默认去注册五个Bean  
![在这里插入图片描述][20200317231255620.png]  
就是如下的五个

1.  internalConfigurationAnnotationProcessor
2.  internalAutowiredAnnotationProcessor
3.  internalCommonAnnotationProcessor
4.  internalEventListenerProcessor
5.  internalEventListenerFactory

最后跟踪发现，它的注册是在AnnotationConfigApplicationContext中的 new AnnotatedBeanDefinitionReader(this)进行的

public AnnotationConfigApplicationContext() {
    		/**
    		 * 实例化reader
    		 * AnnotatedBeanDefinition  被注解的Bean
    		 * 读取那些被加注解了的Bean   会默认去注册那些Spring的内部类
    		 */
    		this.reader = new AnnotatedBeanDefinitionReader(this);
    
    		/**
    		 * 实例化一个scanner
    		 * 能够扫描类，包，并转换为bd
    		 * 这个scan存在的意义就是手动扫描，平时用的@ComponentScan并没有用这个scanner而是又重新new了一个ClassPathBeanDefinitionScanner
    		 */
    		this.scanner = new ClassPathBeanDefinitionScanner(this);
    	}

调用它的构造方法

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
    		this(registry, getOrCreateEnvironment(registry));
    	}
    
    	public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
    		Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    		Assert.notNull(environment, "Environment must not be null");
    		this.registry = registry;
    		this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
    		//AnnotatedBeanDefinitionReader将具体任务交给AnnotationConfigUtils.registerAnnotationConfigProcessors
    		// 注册Spring内部Bean
    		AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
    	}

从而调用AnnotationConfigUtils的registerAnnotationConfigProcessors

/**
    	 * Register all relevant annotation post processors in the given registry.
    	 * @param registry the registry to operate on
    	 *
    	 * 在给定注册表中注册所有相关的注解类的处理器，就是Spring内部的8个内部bean，如果是原生Spring会是5个
    	 *
    	 */
    
    	public static void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
    		registerAnnotationConfigProcessors(registry, null);
    	}

接下来的代码就是最上面的代码了！

[20200317231255620.png]: /images/20230528/adb2b53b5a0c4469953d190ef2b7ee69.png