[pull] master from ipipman:master #21

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	### 通过Java配置Bean的几种方式

	#### 1.通过@Configuration注解注入Bean的方式

	```java
	@Configuration
	public class MyBeanConfiguration {

	/**
	* 通过 @Configuration注解注入一个Bean
	*/
	@Bean("dog")
	public Animal getDog() {
	return new Dog();
	}

	}
	```



	#### 2.通过实现FactoryBean<?>接口的方式注入Bean

	```java
	@Component
	public class MyFactoryBean implements FactoryBean<Animal> {

	/**
	* 返回要注入的类
	*/
	@Override
	public Animal getObject() throws Exception {
	return new Cat();
	}

	/**
	* 获取要注入类的类型
	*/
	@Override
	public Class<?> getObjectType() {
	return Animal.class;
	}

	@Override
	public boolean isSingleton() {
	return FactoryBean.super.isSingleton();
	}

	}
	```



	#### 3.通过实现BeanDefinitionRegistryPostProcessor接口的方式注入Bean

	```java
	@Component
	public class MyBeanDefinitionRegistry implements BeanDefinitionRegistryPostProcessor {

	/**
	* 通过BeanDefinitionRegistryPostProcessor
	*/
	@Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
	RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
	rootBeanDefinition.setBeanClass(Monkey.class);
	beanDefinitionRegistry.registerBeanDefinition("monkey", rootBeanDefinition);
	}

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {

	}
	}
	```



	#### 4.通过实现ImportBeanDefinitionRegistrar接口的方式注入Bean

	```java
	public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

	/**
	* 通过ImportBeanDefinitionRegistrar注入Bean
	*/
	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
	RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
	rootBeanDefinition.setBeanClass(Bird.class);
	registry.registerBeanDefinition("bird", rootBeanDefinition);
	}
	}

	```

	> 使用时:用 @Import(MyImportBeanDefinitionRegistrar.class) 进行注入

276 changes: 276 additions & 0 deletions springboot-source-code-analysis/(12)框架Refresh方法解析一.md

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	### 框架Refresh方法解析一



	#### 1.Refresh方法简介

	- Bean配置读取加载入口
	- Spring框架的启动流程



	#### 2.Refresh方法的执行步骤

	<img src="https://tva1.sinaimg.cn/large/008i3skNly1gvib55enehj61eg0u041602.jpg" alt="image-20211017144834689" align="left" width="800" />

	```java
	@Override
	public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
	// Prepare this context for refreshing.
	// 准备此上下文
	prepareRefresh();

	// Tell the subclass to refresh the internal bean factory.
	// 获取BeanFacotry
	ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

	// Prepare the bean factory for use in this context.
	// 准备此类上下文中使用的Bean工厂
	prepareBeanFactory(beanFactory);

	try {
	// Allows post-processing of the bean factory in context subclasses.
	// 允许在上下文子类中对Bean工厂进行后处理
	postProcessBeanFactory(beanFactory);

	// Invoke factory processors registered as beans in the context.
	// 调用在上下文中注册为Bean的工厂处理器
	invokeBeanFactoryPostProcessors(beanFactory);

	// Register bean processors that intercept bean creation.
	// 注册拦截Bean创建的Bean处理器
	registerBeanPostProcessors(beanFactory);

	// Initialize message source for this context.
	// 为此上下文初始化消息源
	initMessageSource();

	// Initialize event multicaster for this context.
	// 为此上下文初始化事件广播器
	initApplicationEventMulticaster();

	// Initialize other special beans in specific context subclasses.
	// 初始化特定上下文子类中的其他特殊Bean
	onRefresh();

	// Check for listener beans and register them.
	// 检查监听器,并注册
	registerListeners();

	// Instantiate all remaining (non-lazy-init) singletons.
	// 实例化所有剩余的(非延迟初始化)单例。
	finishBeanFactoryInitialization(beanFactory);

	// Last step: publish corresponding event.
	// 最后一步:发布相应的事件
	finishRefresh();
	}

	catch (BeansException ex) {
	if (logger.isWarnEnabled()) {
	logger.warn("Exception encountered during context initialization - " +
	"cancelling refresh attempt: " + ex);
	}

	// Destroy already created singletons to avoid dangling resources.
	// 销毁已经创建的单例以避免浪费资源
	destroyBeans();

	// Reset 'active' flag.
	// 重置active标志
	cancelRefresh(ex);

	// Propagate exception to caller.
	throw ex;
	}

	finally {
	// Reset common introspection caches in Spring's core, since we
	// might not ever need metadata for singleton beans anymore...
	// 重置 Spring 核心中的常见内省缓存,因为我们可能不再需要单例 bean 的元数据...
	resetCommonCaches();
	}
	}
	}
	```



	#### 3.准备上下文:prepareRefersh#方法

	- prepareRefersh#方法简介
	- 清除本地元数据缓存
	- 准备框架上下文
	- 设置框架启动时间
	- 设置框架 active 启动状态为true
	- 如果是Debug模式打印Debug日志
	- 初始化环境配置
	- 获取当前环境配置
	- 如果是Web环境,配置ServletContext 和 ServletConfig
	- 检查环境配置中的必备属性是否存在
	- 如果没有早期的事件监听器,就注册应用监听器:applicationListeners

	- prepareRefresh#方法

	```java
	@Override
	protected void prepareRefresh() {
	// 清除元数据缓存
	this.scanner.clearCache();
	// 准备上下文
	super.prepareRefresh();
	}
	```

	- clearCache#方法

	```java
	/**
	* Clear the local metadata cache, if any, removing all cached class metadata.
	* 清除本地元数据缓存(如果有),删除所有缓存的类元数据。
	*/
	public void clearCache() {
	if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) {
	// Clear cache in externally provided MetadataReaderFactory; this is a no-op
	// for a shared cache since it'll be cleared by the ApplicationContext.
	// 清除外部提供的 MetadataReaderFactory 中的缓存;这是一个无操作用于共享缓存,因为它将被 ApplicationContext 清除。
	((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache();
	}
	}
	```

	- super.prepareRefresh方法

	```java
	/**
	* Prepare this context for refreshing, setting its startup date and
	* active flag as well as performing any initialization of property sources.
	* 准备此上下文以进行刷新、设置其启动日期和* active 标志以及执行属性源的任何初始化
	*/
	protected void prepareRefresh() {
	// Switch to active.
	// 设置启动时间
	this.startupDate = System.currentTimeMillis();
	this.closed.set(false);
	// 设置 active 标志状态为 true
	this.active.set(true);

	// 如果当前日志状态是Debug模式的话,会打印一段话
	if (logger.isDebugEnabled()) {
	if (logger.isTraceEnabled()) {
	logger.trace("Refreshing " + this);
	}
	else {
	logger.debug("Refreshing " + getDisplayName());
	}
	}

	// Initialize any placeholder property sources in the context environment.
	// 初始化环境配置
	initPropertySources();

	// Validate that all properties marked as required are resolvable:
	// see ConfigurablePropertyResolver#setRequiredProperties
	// 检查环境属性中必备的环境数据,如果没有就 throw MissingRequiredPropertiesException 异常
	getEnvironment().validateRequiredProperties();

	// Store pre-refresh ApplicationListeners...
	// 将系统的事件监听器进行注册
	if (this.earlyApplicationListeners == null) {
	this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
	}
	else {
	// Reset local application listeners to pre-refresh state.
	this.applicationListeners.clear();
	this.applicationListeners.addAll(this.earlyApplicationListeners);
	}

	// Allow for the collection of early ApplicationEvents,
	// to be published once the multicaster is available...
	this.earlyApplicationEvents = new LinkedHashSet<>();
	}

	```

	- initPropertySources#方法

	```java
	protected void initPropertySources() {
	// 获取环境配置上下文
	ConfigurableEnvironment env = this.getEnvironment();
	// 如果当前环境是Web环境,将servletContext 和 ServletConfig 加载到环境配置上下文中
	if (env instanceof ConfigurableWebEnvironment) {
	((ConfigurableWebEnvironment)env).initPropertySources(this.servletContext, (ServletConfig)null);
	}
	}
	```





	#### 获取新的Bean工厂:obtainFreshBeanFacotry#方法

	- obtainFreshBeanFacotry#方法简介
	- 设置当前上下文刷新状态为true
	- 这是BeanFactory序列化ID(默认是application)
	- 返回BeanFacotry

	- obtainFreshBeanFactory#方法

	```java
	/**
	* Tell the subclass to refresh the internal bean factory.
	* 告诉子类刷新内部 bean 工厂
	* @return the fresh BeanFactory instance
	* @see #refreshBeanFactory()
	* @see #getBeanFactory()
	*/
	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	// 设置上下文刷新状态和Beanfacotory的序列化ID
	refreshBeanFactory();
	// 获取BeanFactory(默认是DefaultListableBeanFacotry)
	return getBeanFactory();
	}

	```

	- refreshBeanFacoty#方法

	```java
	/**
	* Do nothing: We hold a single internal BeanFactory and rely on callers
	* to register beans through our public methods (or the BeanFactory's).
	* @see #registerBeanDefinition
	*/
	@Override
	protected final void refreshBeanFactory() throws IllegalStateException {
	// 设置当前上下文刷新状态:true
	if (!this.refreshed.compareAndSet(false, true)) {
	throw new IllegalStateException(
	"GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
	}
	// 设置BeanFacotry序列化ID:默认是application
	this.beanFactory.setSerializationId(getId());
	}
	```

	- getBeanFacotory#方法

	```java
	/**
	* Return the single internal BeanFactory held by this context
	* (as ConfigurableListableBeanFactory).
	*/
	@Override
	public final ConfigurableListableBeanFactory getBeanFactory() {
	// 返回默认的 DefaultListableBeanFacotry
	return this.beanFactory;
	}
	```

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