Spring源码解析之Configuration
<!--logback-test.xml，配置不打印日志--><?xml version='1.0' encoding='UTF-8'?><configuration> <include resource='org/springframework/boot/logging/logback/base.xml' /> <logger name='org.springframework' level='OFF'/></configuration>
@Overridepublic void refresh() throws BeansException, IllegalStateException {// 同步，线程安全； 防止 fresh还没结束 就又进入改方法 导致容器初始化错乱synchronized (this.startupShutdownMonitor) {// 准备刷新 记录开始时间 设置几个标志位 验证环境属性prepareRefresh(); // 告诉子类刷新内部bean工厂 创建BeanFactory 并且获取BeanDefinition的定义信息/** *obtainFreshBeanFactory();方法 *解析为一个个beanDefinition 放在我们beanDefinitionMap中管理起来 * 1. refreshBeanFactory(); 核心方法 * AbstractRefreshableApplicationContext#refreshBeanFactory() * 创建DefaultListableBeanFactory 并设置属性 * 加载BeanFactory； 根据不同的类型，调用不同的方法 * org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.support.DefaultListableBeanFactory) */ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // 准备在这种情况下使用的bean工厂 向beanFactory中设置一些属性 。对BeanFactory 进行各种功能填充prepareBeanFactory(beanFactory); try {// 允许在上下文 的子类中对bean工厂进行后处理 由子类去实现； 主要是自定义去使用postProcessBeanFactory(beanFactory); // 第5步 【BeanFactoryPostProcessors ;bean工厂后置处理器】调用我们的bean工厂后置处理器 (所有实现接口BeanFactoryPostProcessor接口的)//主要是// 会在此将class扫描成BeanDefinition 并注册bean 到一个BeanDefinitionMap中 这个过程使用到代理//BeanFactoryPostProcessor 可以 用于容器完成初始化()// 此处可以 还没有实例化Bean之前读取Bean的信息，并作出一些修改。// 例如修改Bean的属性，修改Bean的scope等invokeBeanFactoryPostProcessors(beanFactory); //https://blog.csdn.net/caihaijiang/article/details/35552859// 【BeanPostProcessors ;bean后置处理器】 注册BeanPostProcessor// BeanPostProcessor是Bean的后置处理器，// 在Bean的初始化方法[InitializingBean 以及init-method]前，后执行。registerBeanPostProcessors(beanFactory); // 为上下文初始化Message 源， 即不同语言的消息体， 国际化处理 i18ninitMessageSource(); // 初始化事件传播器//初始化应用消息广播器， 并放入'applicationEventMulticaster' bean 中initApplicationEventMulticaster(); // 扩展的一个实现 ，留给子类来初始化其它的Bean。如springboot内嵌的tomcat在这个阶段完成onRefresh(); // 注册监听器// 在所有注册的bean 中查找Listener bean ， 注册到消息广播报中registerListeners(); /**第11步对于非抽象类、非延迟初始化的单例bean，在spring容器启动的时候调用getBean方法来实例化bean， 并进行相关初始化工作，getBean方法最终调用AbstractAutowireCapableBeanFactory.doCreateBean方法 */// 在创建BeanFactory的过程中，BeanDefinition注册到了BeanFactory中的一个ConCurretHashMap对象中// 以BeanName为key，BeanDefinition为value ； 实例化所有剩余的（非延迟初始化）单例。finishBeanFactoryInitialization(beanFactory); // 第12步 最后一步：发布相应的事件。//完成刷新过程， 通知生命周期处现器lifecycleProcessor 刷新过程， 同时发出ContextRefreshEvent 通知别人finishRefresh();} catch (BeansException ex) {if (logger.isWarnEnabled()) {logger.warn('Exception encountered during context initialization - ' +'cancelling refresh attempt: ' + ex);} // 第13步 销毁以创建的BeandestroyBeans(); //取消refresh操作，重置容器的同步标识cancelRefresh(ex); // Propagate exception to caller.throw ex;} finally {resetCommonCaches();}}}2.4 AbstractApplicationContext#invokeBeanFactoryPostProcessors
public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) { Set<String> processedBeans = new HashSet<>(); // 对BeanDefinitionRegistry 类型的处理if (beanFactory instanceof BeanDefinitionRegistry) {BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();// 用于存放BeanDefinitionRegistryPostProcessorList<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>(); // 遍历所有的beanFactoryPostProcessors，将BeanDefinitionRegistryPostProcessor和普通BeanFactoryPostProcessor区分开for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {BeanDefinitionRegistryPostProcessor registryProcessor =(BeanDefinitionRegistryPostProcessor) postProcessor;/**对于BeanDefinitionRegistryPostProcessor 类型， 在BeanFactoryPostProcessor 的基础上还有自己定义的方法，需要先调用 */registryProcessor.postProcessBeanDefinitionRegistry(registry);registryProcessors.add(registryProcessor);}else {// 记录常规BeanFactoryPostProcessorregularPostProcessors.add(postProcessor);}} /**不要在这里初始化FactoryBeans: 我们需要保留所有常规bean未初始化，让bean工厂后处理器应用到它们!BeanDefinitionRegistryPostProcessors之间的分离实现排好序，点好，等等。获取spring配置文件中定义的所有实现BeanFactoryPostProcessor接口的bean，然后根据优先级进行排序 */List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>(); // 首先，调用实现优先排序的BeanDefinitionRegistryPostProcessorsString[] postProcessorNames =beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {// PriorityOrdered.class 优先排序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);currentRegistryProcessors.clear(); // 接下来，调用实现Ordered的BeanDefinitionRegistryPostProcessorspostProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {// Ordered.classif (!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);currentRegistryProcessors.clear(); // 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);currentRegistryProcessors.clear();} // Now, invoke the postProcessBeanFactory callback of all processors handled so far.// 调用ConfigurationClassPostProcessor#postProcessBeanFactory增强配置类// 通过cglib生成增强类// 设置beanDefinition的beanClass为增强类，让@Bean生成的bean是单例invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);} else {// Invoke factory processors registered with the context instance.invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);} // BeanFactoryPostProcessor.class类型// 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);// 筛选出bean工程中存在的所有实现BeanFactoryPostProcessor类的类名称 // 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// 已经存在了，不再处理}else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {// 为PriorityOrdered类型priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));}else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {// 为Ordered类型orderedPostProcessorNames.add(ppName);}else {// 这个就是我们当前需要关心的PostProcessors//nonOrderedPostProcessors添加的不是bean实例，而是BeanDefinitionnonOrderedPostProcessorNames.add(ppName);}} // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.sortPostProcessors(priorityOrderedPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered.List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();for (String postProcessorName : orderedPostProcessorNames) {orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}sortPostProcessors(orderedPostProcessors, beanFactory);invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); // Finally, invoke all other BeanFactoryPostProcessors.List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();for (String postProcessorName : nonOrderedPostProcessorNames) {nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));}invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory); // Clear cached merged bean definitions since the post-processors might have// modified the original metadata, e.g. replacing placeholders in values...beanFactory.clearMetadataCache();}2.6 PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors
public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<>();for (String beanName : beanFactory.getBeanDefinitionNames()) {BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);// 判断是否是一个全注解类// 扫描是全注解类？full和lite的关系if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) {if (!(beanDef instanceof AbstractBeanDefinition)) {throw new BeanDefinitionStoreException('Cannot enhance @Configuration bean definition ’' +beanName + '’ since it is not stored in an AbstractBeanDefinition subclass');}else if (logger.isInfoEnabled() && beanFactory.containsSingleton(beanName)) {logger.info('Cannot enhance @Configuration bean definition ’' + beanName +'’ since its singleton instance has been created too early. The typical cause ' +'is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor ' +'return type: Consider declaring such methods as ’static’.');}// 是全注解，需要代理，添加到configBeanDefs中configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);}}if (configBeanDefs.isEmpty()) {// nothing to enhance -> return immediatelyreturn;} ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();// 遍历这个mapfor (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {AbstractBeanDefinition beanDef = entry.getValue();// If a @Configuration class gets proxied, always proxy the target classbeanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);try {// Set enhanced subclass of the user-specified bean classClass<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);if (configClass != null) {// 进行cglib代理，为@Configuration注解的类生成增强类Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);if (configClass != enhancedClass) {if (logger.isTraceEnabled()) {logger.trace(String.format('Replacing bean definition ’%s’ existing class ’%s’ with ' +'enhanced class ’%s’', entry.getKey(), configClass.getName(), enhancedClass.getName()));}// 再通过beanDef.setBeanClass(enhancedClass)修改beanDefinition的BeanClass属性，// 在bean实例化阶段，会利用反射技术将beanClass属性对应的类实例化出来// 所以最终实例化出来的@Configuration bean是一个代理类的实例beanDef.setBeanClass(enhancedClass);}}}catch (Throwable ex) {throw new IllegalStateException('Cannot load configuration class: ' + beanDef.getBeanClassName(), ex);}}
1.在ConfigurationClassUtils类中的checkConfigurationClassCandidate标记是Full @Configuration还是lite @Bean mode
2.通过'full'.equals(configClassAttr)判断是否是全类注解是全注解
3.则将beandefinition放入map中configBeanDefs.put
4.遍历这个map
5.使用cglib技术为配置类生成一个enhancedClass
6.通过enhancer.enhance进行cglib代理，为@Configuration注解的类生成增强类
7.再通过beanDef.setBeanClass(enhancedClass)修改beanDefinition的BeanClass属性，在bean实例化阶段，会利用反射技术将beanClass属性对应的类实例化出来，所以最终实例化出来的@Configuration bean是一个代理类的实例
使用了@Configuration注解的类，属于Full @Configuration。@Configuration类允许通过调用同一类中的其他@Bean方法来定义bean之间的依赖关系，保证@Bean的对象作用域受到控制，避免多例。
@Configuration类中的@Bean地方会被CGLIB进行代理。Spring会拦截该方法的执行，在默认单例情况下，容器中只有一个Bean，所以我们多次调用user()方法，获取的都是同一个对象。
对于@Configuration注解的类中@Bean标记的方法，返回的都是一个bean，在增强的方法中，Spring会先去容器中查看一下是否有这个bean的实例了，如果有了的话，就返回已有对象，没有的话就创建一个，然后放到容器中。
2.10 ConfigurationClassEnhancer#enhance
private Object resolveBeanReference(Method beanMethod, Object[] beanMethodArgs,ConfigurableBeanFactory beanFactory, String beanName) { // The user (i.e. not the factory) is requesting this bean through a call to// the bean method, direct or indirect. The bean may have already been marked// as ’in creation’ in certain autowiring scenarios; if so, temporarily set// the in-creation status to false in order to avoid an exception.// 判断他是否正在创建boolean alreadyInCreation = beanFactory.isCurrentlyInCreation(beanName);try {if (alreadyInCreation) {beanFactory.setCurrentlyInCreation(beanName, false);}boolean useArgs = !ObjectUtils.isEmpty(beanMethodArgs);if (useArgs && beanFactory.isSingleton(beanName)) {// Stubbed null arguments just for reference purposes,// expecting them to be autowired for regular singleton references?// A safe assumption since @Bean singleton arguments cannot be optional...for (Object arg : beanMethodArgs) {if (arg == null) {useArgs = false;break;}}}Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) :beanFactory.getBean(beanName));if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) {// Detect package-protected NullBean instance through equals(null) checkif (beanInstance.equals(null)) {if (logger.isDebugEnabled()) {logger.debug(String.format('@Bean method %s.%s called as bean reference ' +'for type [%s] returned null bean; resolving to null value.',beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),beanMethod.getReturnType().getName()));}beanInstance = null;}else {String msg = String.format('@Bean method %s.%s called as bean reference ' +'for type [%s] but overridden by non-compatible bean instance of type [%s].',beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),beanMethod.getReturnType().getName(), beanInstance.getClass().getName());try {BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName);msg += ' Overriding bean of same name declared in: ' + beanDefinition.getResourceDescription();}catch (NoSuchBeanDefinitionException ex) {// Ignore - simply no detailed message then.}throw new IllegalStateException(msg);}}Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod();if (currentlyInvoked != null) {String outerBeanName = BeanAnnotationHelper.determineBeanNameFor(currentlyInvoked);beanFactory.registerDependentBean(beanName, outerBeanName);}return beanInstance;}finally {if (alreadyInCreation) {beanFactory.setCurrentlyInCreation(beanName, true);}}}三、总结 lite @Bean mode ：当@Bean方法在没有使用@Configuration注解的类中声明时称之为lite @Bean mode Full @Configuration：如果@Bean方法在使用@Configuration注解的类中声明时称之为Full @Configuration
Full @Configuration中的@Bean方法会被CGLIB所代理，而 lite @Bean mode中的@Bean方法不会被CGLIB代理
@Configuration注解作用
1.告诉spring这是一个配置类，相当于spring的xml配置文件
2.被@Configuration 注解的类，会被cglib代理进行增强
3.@Configuration类允许通过调用同一类中的其他@Bean方法来定义bean之间的依赖关系，保证@Bean的对象作用域受到控制，避免多例
@Configuration注解底层是如何实现的，通过源码咱们可以反推并总结为以下几点：
1.Spring首先会获取到所有的beanDefenition
2.ConfigurationClassUtils类中checkConfigurationClassCandidate方法判断是Full @Configuration还是lite @Bean mode
3.通过ConfigurationClassPostProcessor后置处理器遍历所有的beanDefenition
4.将标记了Full @Configuration模式的beanDefenition，会对这个类进行cglib代理，生成一个代理类，并把这个类设置到BeanDefenition的Class属性中
5.配置类会被CGLIB增强(生成代理对象)，放进IoC容器内的是代理
6.对于内部类是没有限制的：可以是Full模式或者Lite模式
7.配置类内部可以通过方法调用来处理依赖，并且能够保证是同一个实例，都指向IoC内的那个单例
8.需要用这个Bean实例的时候，从这个Class属性中拿到的Class对象进行反射，最终反射出来的是代理增强后的类
9.通过@Configuration标注类的Bean，Spring会先去容器中查看是否有这个Bean实例，如果有就返回已有的对象，没有就创建一个，然后放到容器中
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