Spring(二)Spring IOC

IOC(Inversion of Control)和DI(Dependecy Injection)，IOC控制反转，由Spring来控制管理对象的生命周期和对象间的关系。将对象交给容器来创建，程序不再创建；DI依赖注入，容器创建对象时，容器将对象的依赖注入到对象中。Spring以这两种思想来实现对Bean的管理。继而实现松耦合。

首先了解一下关键API

BeanFactory，接口，Spring Bean容器顶级接口，提供访问Bean容器的的基本接口。类和接口的关系如下：

ApplicationContext，接口，为应用提供配置的核心接口。类和结构的关系如下。

通常，我们启动Spring容器就是初始化一个ApplicationContext的实例，比如new ClassPathXmlApplicationContext();随着ApplicationContext的实例化，Spring容器也相应的创建。所以下来通过ApplicationContext的实例化来了解Spring容器的启动过程。

同时，SpringBoot应用启动的API，SpringApplication.run()，在启动的过程中，根据参数args，初始化不同的ApplicationContext实现，源码如下：

protected ConfigurableApplicationContext createApplicationContext() {
	Class contextClass = this.applicationContextClass;
    //首先根据配置，没有配置取默认的ApplicationContext
	if (contextClass == null) {
		try {
			switch (this.webApplicationType) {
			case SERVLET:
                //加载AnnotationConfigServletWebServerApplicationContext
				contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
				break;
			case REACTIVE:
                //加载AnnotationConfigServletWebServerApplicationContext
				contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
				break;
			default:
                //加载AnnotationConfigApplicationContext
				contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
			}
		}
		catch (ClassNotFoundException ex) {
			throw new IllegalStateException(
					"Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass",
					ex);
		}
	}
    //创建ApplicationContext实例
	return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

默认的AnnotationConfigApplicationContext是基于注解的，基于注解的配置也被大多数人所接受，所以我们通过实例化AnnotationConfigApplicationContext来启动Spring容器，进一步了解Spring。

启动Spring容器测试以及

public class SpringTest {

    public static void main(String[] args) {
        //初始化Spring容器
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
        //扫描包com.weihao
        applicationContext.scan("com.weihao");
        //加载配置
        applicationContext.refresh();
        //通过ApplicationContext获取TestService实例
        TestService testService = (TestService) applicationContext.getBean("testService");
        //调用TestService方法
        testService.sayHello();
    }
}

TestService源码

@Component
public class TestService {

    public void sayHello(){
        System.out.println("hello world");
    }
}

AnnotationConfigApplicationContext初始化

接下来看一下AnnotationConfigApplicationContext 启动时，都做了那些事情。AnnotationConfigApplicationContext源码构造器。

//创建一个AnnotationConfigApplicationContext， 需要调用#register填充，手动调用#refresh刷新
public AnnotationConfigApplicationContext() {
	this.reader = new AnnotatedBeanDefinitionReader(this);
	this.scanner = new ClassPathBeanDefinitionScanner(this);
}

构造器中AnnotationConfigApplicationContext使用自己作为参数，初始化了AnnotatedBeanDefinitionReader和ClassPathBeanDefinitionScanner两个对象，并传给成员变量。其中AnnotationConfigApplicationContext实现了BeanDefinitionRegistry接口，作为registry对象去初始化两个成员变量。AnnotatedBeanDefinitionReader根据文档，功能是注册基于注解的bean的，ClassPathBeanDefinitionScanner是在classpath扫描BeanDefinition，注册扫描到的BeanDefinition。

BeanDefinition，顾名思义，就是Bean的定义。

其中AnnotatedBeanDefinitionReader的构造函数中，将AnnotationConfigApplicationContext对象作为registry成员属性，新创建了ConditionEvaluator，并给registry注册相关处理器。

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;
    //@Conditional注解的解析评估
	this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
    //将注解配置处理器注册到Registry
	AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

ConditionEvaluator，用来解析评估@Conditional注解。

在给定的Registry中注册相关注解配置处理器。处理逻辑如下。

public static Set registerAnnotationConfigProcessors(
		BeanDefinitionRegistry registry, @Nullable Object source) {
    //取出BeanFactory，AnnotationConfigApplicationContext继承自GenericApplicationContext，
    //具有DefaultListableBeanFactory的属性。
	DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
	if (beanFactory != null) {
        // 依赖比较器
		if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
			beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
		}
        // 自动装配解析器
		if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
			beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
		}
	}
    // Bean定义管理器集合
	Set beanDefs = new LinkedHashSet<>(8);
    // @Configuration注解的引导处理器，按照优先级排序的，因为在@Configuration类中声明的任何
    // Bean方法，都必须在其他类之前将BeanDefinition注册到Registry
	if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
		RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
		def.setSource(source);
		beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
	}
    //1, 自动装备带注解的字段、setter方法、任意配置方法，要注入的这些成员都是通过Java5注解检测,
    // 默认情况下Spring的@Autowire注解和@Value注解，如果可用，也支持JSR-330的注解，@Inject
    //2,任何给定bean类，只有一个构造函数是，可以声明这个注解，且require参数设置为true，指示
    //构造函数自动装备Bean。如果有多个构造函数，他们被当做自动装备候选，有最多依赖的构造函数且
    //可以在Spring容器中匹配所有依赖的构造函数，会被选择为自动装备构造函数。如果没有一个候选构造
    //函数满足，会选择默认的构造函数，如果类只声明了一个构造函数，即使没有注解也会使用被使用。
    //带注解的构造函数不需要声明为public
	if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
		RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
		def.setSource(source);
		beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
	}

	//检查支持JSR-250, 如果类的路径中包含JSR-250注解，添加CommonAnnotationBeanPostProcessor
    //1,支持开箱即用的Java注解，JSR-250的注解，即javax.annotation包中的注解
    //2,同时继承了InitDestroyAnnotationBeanPostProcessor，支持@PostConstruct，@PreDestroy
    //3,支持JAX-WS注解，EJB3注解，可以同时指定本地名称和全局JNDI检索名称
    //4,对于直接的JNDI访问，使用JavaEE应用的java:/comp/env命名空间中的JNDI资源引用，来解析
    //资源名称
	if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
		RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
		def.setSource(source);
		beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
	}

    //检查JPA支持, 如果包含，增加PersistenceAnnotationBeanPostProcessor.
    //处理PersistenceUnit和PersistenceContext注解，注入相应的JPA资源，EntityManagerFactory
    //, EntityManager,自动注入任何SpringBean中有此注解的字段，方法
	if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
		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));
	}
    //注册@EventListener为单独的实例
	if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
		RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
		def.setSource(source);
		beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
	}
    //支持常规的注解实现
	if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
		RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
		def.setSource(source);
		beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
	}

	return beanDefs;
}

再来看看这些注解解析处理器是怎么注册的，源码如下

private static BeanDefinitionHolder registerPostProcessor(
		BeanDefinitionRegistry registry, RootBeanDefinition definition, String beanName) {
    //指定bean的角色
    //ROLE_APPLICATION=0,Bean是应用的主要的一部分，通常对应用户自定义的Bean。
    //ROLE_SUPPORT=1,Bean是一些比较大的配置支持部分，通常是外部的ComponentDefinition。
    //ROLE_INFRASTRUCTURE=2,表明提供完全的后台角色，且与最终用户无关，注册完全属于
    //ComponetDefinitionn内部工作的Bean时使用
	definition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	//注册，bean名称和bean定义
    registry.registerBeanDefinition(beanName, definition);
    //返回Bean定义holder对象
	return new BeanDefinitionHolder(definition, beanName);
}

进一步注册，源码如下。

@Override
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
		throws BeanDefinitionStoreException {

	Assert.hasText(beanName, "Bean name must not be empty");
	Assert.notNull(beanDefinition, "BeanDefinition must not be null");
    //验证
	if (beanDefinition instanceof AbstractBeanDefinition) {
		try {
			((AbstractBeanDefinition) beanDefinition).validate();
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
					"Validation of bean definition failed", ex);
		}
	}
    //
	BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
    //如果已经包含名称为BeanName的Bean定义
	if (existingDefinition != null) {
        //如果不允许覆盖，抛出异常
		if (!isAllowBeanDefinitionOverriding()) {
			throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
		}
        //如果允许覆盖，且存在的角色小于目前bean的角色
		else if (existingDefinition.getRole() < beanDefinition.getRole()) {
			// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
			if (logger.isInfoEnabled()) {
				logger.info("Overriding user-defined bean definition for bean '" + beanName +
						"' with a framework-generated bean definition: replacing [" +
						existingDefinition + "] with [" + beanDefinition + "]");
			}
		}
        //如果允许覆盖，且角色存在的大于等于目前Bean角色，且目前Bean定义不等于存在的Bean定义
		else if (!beanDefinition.equals(existingDefinition)) {
			if (logger.isDebugEnabled()) {
				logger.debug("Overriding bean definition for bean '" + beanName +
						"' with a different definition: replacing [" + existingDefinition +
						"] with [" + beanDefinition + "]");
			}
		}
        // 覆盖
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("Overriding bean definition for bean '" + beanName +
						"' with an equivalent definition: replacing [" + existingDefinition +
						"] with [" + beanDefinition + "]");
			}
		}
		this.beanDefinitionMap.put(beanName, beanDefinition);
	}
    // 原来的BeanDefinition等于null，覆盖
	else {
        //开始创建Bean了
		if (hasBeanCreationStarted()) {
			// Cannot modify startup-time collection elements anymore (for stable iteration)
			synchronized (this.beanDefinitionMap) {
				this.beanDefinitionMap.put(beanName, beanDefinition);
				List updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
				updatedDefinitions.addAll(this.beanDefinitionNames);
				updatedDefinitions.add(beanName);
				this.beanDefinitionNames = updatedDefinitions;
				removeManualSingletonName(beanName);
			}
		}
		else {
			// Still in startup registration phase
			this.beanDefinitionMap.put(beanName, beanDefinition);
			this.beanDefinitionNames.add(beanName);
			removeManualSingletonName(beanName);
		}
		this.frozenBeanDefinitionNames = null;
	}

	if (existingDefinition != null || containsSingleton(beanName)) {
		resetBeanDefinition(beanName);
	}
}

接下来看AnnotationConfigApplicationContext的另一个属性ClassPathBeanDefinitionScanner，在AnnotationConfigApplicationContext实例化时，都做了那些事情。

/**
 * registry，AnnotationConfigApplicationContext实现了DefinitionRegistry接口，即自己本身
 * userDefaultFilters，true
 * environment，AnnotationConfigApplicationContext实现了EnvironmentCapable，即自己的属性
 * resourceLoader，AnnotationConfigApplicationContext实现了ResourceLoader，即自己本身
 */
public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
		Environment environment, @Nullable ResourceLoader resourceLoader) {

	Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
	this.registry = registry;

	if (useDefaultFilters) {
        //注册默认的过滤器，包括@Componet注解，和所有具有@Componet注解的注解
		registerDefaultFilters();
	}
	setEnvironment(environment);
	setResourceLoader(resourceLoader);
}

注册默认过滤器，扫描过滤注解类，在扫描注解配置的时候会用到。源码如下：

/**
 * 注册@Component默认的filter，将会注册所有的注解包含@Componet注解的注解，包括@Repository，
 * @Service，@Controller，也支持JavaEE6的ManageBean，JSR-330的@Named注解，如果可用的话
 */
@SuppressWarnings("unchecked")
protected void registerDefaultFilters() {
    //添加@Componet注解的filter
	this.includeFilters.add(new AnnotationTypeFilter(Component.class));
	ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
	try {
        //添加JSR-250注解filter
		this.includeFilters.add(new AnnotationTypeFilter(
				((Class) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
		logger.trace("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
	}
	catch (ClassNotFoundException ex) {
		// JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
	}
	try {
        //添加JSR-330注解filter
		this.includeFilters.add(new AnnotationTypeFilter(
				((Class) ClassUtils.forName("javax.inject.Named", cl)), false));
		logger.trace("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
	}
	catch (ClassNotFoundException ex) {
		// JSR-330 API not available - simply skip.
	}
}

在设置ResourceLoader的过程中，还初始化了ResourcePatternResolver，源码如下：

@Override
public void setResourceLoader(@Nullable ResourceLoader resourceLoader) {
    // resourceLoader本身实现了ResourcePatternResolver，就使用本身，否则创建一个默认的
	this.resourcePatternResolver = ResourcePatternUtils.getResourcePatternResolver(resourceLoader);
    // 元数据读取工厂
	this.metadataReaderFactory = new CachingMetadataReaderFactory(resourceLoader);
    // 提供对候选的访问，如获取com.weihao包下面的所有的@Component候选，
    // candidates = index.getCandidateTypes("com.weihao", 
    // "org.springframework.stereotype.Component")
	this.componentsIndex = CandidateComponentsIndexLoader.loadIndex(this.resourcePatternResolver.getClassLoader());
}

scan过程

在AnnotationConfigApplicationContext初始化之后，就是指定包名称，调用scan扫描配置的过程了,我们接下来看一下scan都做了哪些事情。调用scan的源码如下。

public void scan(String... basePackages) {
	Assert.notEmpty(basePackages, "At least one base package must be specified");
    //实际上是调用了ClassPathBeanDefinitionScanner来扫描
	this.scanner.scan(basePackages);
}

根据源码可以看到，实际上调用了ClassPathBeanDefinitionScanner来扫描Bean定义的。

public int scan(String... basePackages) {
    //获取scan之前的BeanDefinition数量
	int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
    //扫描包
	doScan(basePackages);
    
    // 注册注解配置处理器，如果必要的话
	// Register annotation config processors, if necessary.
	if (this.includeAnnotationConfig) {
		AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
	}
    //返回新扫描的BeanDefinition
	return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
}

根据上面的代码，具体的逻辑在doScan中，源码如下。

protected Set doScan(String... basePackages) {
	Assert.notEmpty(basePackages, "At least one base package must be specified");
	// BeanDefinition Holder集合
	Set beanDefinitions = new LinkedHashSet<>();
	// 遍历包
	for (String basePackage : basePackages) {
		//查找候选的BeanDefinition集合
		Set candidates = findCandidateComponents(basePackage);
		//遍历候选BeanDefinition集合
		for (BeanDefinition candidate : candidates) {
			// 获取scop源数据
			ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
			candidate.setScope(scopeMetadata.getScopeName());
			String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
                    // 设置更多的配置，一般是Bean的默认配置，lazyInit，initMethodName，destoryMethodName等
			if (candidate instanceof AbstractBeanDefinition) {
				postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
			}
                    // 设置通用的注解配置，lazyInit，primary等
			if (candidate instanceof AnnotatedBeanDefinition) {
                              AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
			}
			// 检查bean定义，bean名称，查看是否需要注册或者和存在的bean定义冲突
			if (checkCandidate(beanName, candidate)) {
				//创建Bean定义 Holder
				BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
				// 处理scope，主要是target class proxy
				definitionHolder =
						AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
				// 添加到BeanDefinitionHolder
				beanDefinitions.add(definitionHolder);
				//注册
				registerBeanDefinition(definitionHolder, this.registry);
			}
		}
	}
	//返回BeanDefinition Holder集合
	return beanDefinitions;
}

根据上面的代码，可以看到扫描到的BeanDefinition已经被注册到了Registry，看一下Spring如何查找候选的BeanDefinition集合，findCandidateComponents方法源码如下：

/**
 * 在classpath扫描候选的componets
 * @param basePackage 检查注解类的包
 * @return 返回自动检查的相应的BeanDefinition集合
 */
public Set findCandidateComponents(String basePackage) {
	if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
        //使用索引，在索引上添加查询 类和注解的相关信息
		return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
	}
	else {
        //扫描
		return scanCandidateComponents(basePackage);
	}
}

查看具体的扫描，scanCandidateComponents，源码如下：

private Set scanCandidateComponents(String basePackage) {
	Set candidates = new LinkedHashSet<>();
	try {
        //包路径转为资源路径
		String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
				resolveBasePackage(basePackage) + '/' + this.resourcePattern;
        //获取资源
		Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
		boolean traceEnabled = logger.isTraceEnabled();
		boolean debugEnabled = logger.isDebugEnabled();
		for (Resource resource : resources) {
			if (traceEnabled) {
				logger.trace("Scanning " + resource);
			}
			if (resource.isReadable()) {
				try {
                    //获取元数据
					MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
					if (isCandidateComponent(metadataReader)) {
                        //创建BeanDefinition
						ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
						sbd.setResource(resource);
						sbd.setSource(resource);
						if (isCandidateComponent(sbd)) {
							if (debugEnabled) {
								logger.debug("Identified candidate component class: " + resource);
							}
							candidates.add(sbd);
						}
						else {
							if (debugEnabled) {
								logger.debug("Ignored because not a concrete top-level class: " + resource);
							}
						}
					}
					else {
						if (traceEnabled) {
							logger.trace("Ignored because not matching any filter: " + resource);
						}
					}
				}
				catch (Throwable ex) {
					throw new BeanDefinitionStoreException(
							"Failed to read candidate component class: " + resource, ex);
				}
			}
			else {
				if (traceEnabled) {
					logger.trace("Ignored because not readable: " + resource);
				}
			}
		}
	}
	catch (IOException ex) {
		throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
	}
	return candidates;
}

其中扫描BeanDefinition有很多细节，如果仔细研究，也有非常大的一部分。这里就不在赘述。

扫描完成后，接下来将扫描到的BeanDefinition注册到Registry，源码和初始化AnnotationConfigApplicationContext时的注册相同，如下。这里就不在贴源码了。

所以，scan的过程结束后，BeanDefinition也已经注册到了Registry。

refresh过程

在BeanDefinition被注册到Registry后，接下来是refresh的过程，加载，刷新配置，刷新ApplicationContext。接下来通过读源码看一下，applicationContext在refresh过程中都做了哪些事情。refresh源码如下

@Override
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// Prepare this context for refreshing.准备刷新
		prepareRefresh();

		// Tell the subclass to refresh the internal bean factory. 告诉子类刷新内部容器
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// Prepare the bean factory for use in this context.准备BeanFactory
		prepareBeanFactory(beanFactory);

		try {
			// 允许 子类的BeanFactory 完成执行方法
			// Allows post-processing of the bean factory in context subclasses.
			postProcessBeanFactory(beanFactory);
            
			// 执行作为Bean注册在Context的 完成执行方法
			// Invoke factory processors registered as beans in the context.
			invokeBeanFactoryPostProcessors(beanFactory);

			// 拦截Bean创建，注册Bean执行器
            // Register bean processors that intercept bean creation.
			registerBeanPostProcessors(beanFactory);
            
			// 初始化context的消息源
			// Initialize message source for this context.
			initMessageSource();

			// 初始化context的事件广播
			// Initialize event multicaster for this context.
			initApplicationEventMulticaster();

			// 在特殊的context子类中初始化其他特殊的Bean
			// Initialize other special beans in specific context subclasses.
			onRefresh();

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

			// 实例化所有剩余（非lazy-init）单例
			// Instantiate all remaining (non-lazy-init) singletons.
			finishBeanFactoryInitialization(beanFactory);

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

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

			// Propagate exception to caller.
			throw ex;
		}

		finally {
			// 释放缓存，重置Spring中常见缓存，因为不再需要metadata元数据。
			// Reset common introspection caches in Spring's core, since we
			// might not ever need metadata for singleton beans anymore...
			resetCommonCaches();
		}
	}
}

根据refresh的每一步，进一步了解refresh的过程，到底做了什么

prepareRefresh，准备刷新，源码如下。

protected void prepareRefresh() {
	// 设置启动事件，close状态设置为false，active状态设置为true
	this.startupDate = System.currentTimeMillis();
	this.closed.set(false);
	this.active.set(true);
    
	if (logger.isDebugEnabled()) {
		if (logger.isTraceEnabled()) {
			logger.trace("Refreshing " + this);
		}
		else {
			logger.debug("Refreshing " + getDisplayName());
		}
	}
	// 初始化context环境中的占位符属性源
	// Initialize any placeholder property sources in the context environment.
	initPropertySources();

	// 校验被标记为需要的所有属性都可以解析，查看
	// Validate that all properties marked as required are resolvable:
	// see ConfigurablePropertyResolver#setRequiredProperties
	getEnvironment().validateRequiredProperties();

	// 保存预刷新应用监听器
	// Store pre-refresh ApplicationListeners...
	if (this.earlyApplicationListeners == null) {
		this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
	}
	else {
		// 重置本地监听器 为 预刷新状态
		// Reset local application listeners to pre-refresh state.
		this.applicationListeners.clear();
		this.applicationListeners.addAll(this.earlyApplicationListeners);
	}

	// 允许保存早期的，当广播可以时被发布出来应用事件
	// Allow for the collection of early ApplicationEvents,
	// to be published once the multicaster is available...
	this.earlyApplicationEvents = new LinkedHashSet<>();
}

准备刷新的过程中，又包括多步操作，初始化占位符属性元，校验需要的属性，保存预刷新监听器，初始化早期的应用事件集合等操作，细节不在一个一个展开分析了。

准备刷新后，接下来是通知子类刷新内部的BeanFactory。

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	// 刷新BeanFactory
	refreshBeanFactory();
	// 返回BeanFactory
	return getBeanFactory();
}

如何刷新呢，主要是设置刷新状态并返回AnnotationConfigApplicationContext中的属性DefaultListableBeanFactory的实例。

@Override
protected final void refreshBeanFactory() throws IllegalStateException {
	if (!this.refreshed.compareAndSet(false, true)) {
		throw new IllegalStateException(
			"GenericApplicationContext does not support multiple refresh attempts: just call 'refresh' once");
	}
	this.beanFactory.setSerializationId(getId());
}

准备BeanFactory，prepareBeanFactory

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		//通知内部BeanFactory，DefaultListableBeanFactory，使用context的类加载器		
		// Tell the internal bean factory to use the context's class loader etc.
		beanFactory.setBeanClassLoader(getClassLoader());
		beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
		beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
		
		// 使用context回调，配置BeanFactory
		// Configure the bean factory with context callbacks.
		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
		beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
		beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
		beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
		beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
		beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

		// BeanFactory接口未在普通工厂中注册为可解析类型，消息源作为Bean注册并自动装配
		// BeanFactory interface not registered as resolvable type in a plain factory.
		// MessageSource registered (and found for autowiring) as a bean.
		beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
		beanFactory.registerResolvableDependency(ResourceLoader.class, this);
		beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
		beanFactory.registerResolvableDependency(ApplicationContext.class, this);

		// 注册早期 post-processor 以检测内部Bean作为应用监听器
		// Register early post-processor for detecting inner beans as ApplicationListeners.
		beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

		// 检测LoadTimeWeaver 如果发现准备编制
		// Detect a LoadTimeWeaver and prepare for weaving, if found.
		if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
			// Set a temporary ClassLoader for type matching.
			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
		}

		// 注册默认环境Bean
		// Register default environment beans.
		if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
		}
	}

 

获取Bean

获取Bean，即applicationContext.getBean(）方法。源码如下：

    protected  T doGetBean(final String name, @Nullable final Class requiredType,
			@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
		//转变Bean名称        
		final String beanName = transformedBeanName(name);
		Object bean;

		// 检查单例缓存，以是有手动注册单例
		// Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName);
		if (sharedInstance != null && args == null) {
			if (logger.isTraceEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
			// 获取Bean
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else {
            // 如果已经创建了Bean，失败
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// 检查是不是Bean定义在factory中存在
			// Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// 不存在检查 父				
				// Not found -> check parent.
				String nameToLookup = originalBeanName(name);
				if (parentBeanFactory instanceof AbstractBeanFactory) {
					return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
							nameToLookup, requiredType, args, typeCheckOnly);
				}
				else if (args != null) {
					// Delegation to parent with explicit args.
					return (T) parentBeanFactory.getBean(nameToLookup, args);
				}
				else if (requiredType != null) {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
				else {
					return (T) parentBeanFactory.getBean(nameToLookup);
				}
			}

			if (!typeCheckOnly) {
				markBeanAsCreated(beanName);
			}

			try {
				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
				checkMergedBeanDefinition(mbd, beanName, args);

				// Guarantee initialization of beans that the current bean depends on.
				String[] dependsOn = mbd.getDependsOn();
				if (dependsOn != null) {
					for (String dep : dependsOn) {
						if (isDependent(beanName, dep)) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
						}
						registerDependentBean(dep, beanName);
						try {
							getBean(dep);
						}
						catch (NoSuchBeanDefinitionException ex) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
						}
					}
				}

				// Create bean instance.
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);
						}
						catch (BeansException ex) {
							// Explicitly remove instance from singleton cache: It might have been put there
							// eagerly by the creation process, to allow for circular reference resolution.
							// Also remove any beans that received a temporary reference to the bean.
							destroySingleton(beanName);
							throw ex;
						}
					});
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}

				else if (mbd.isPrototype()) {
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
						beforePrototypeCreation(beanName);
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally {
						afterPrototypeCreation(beanName);
					}
					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				else {
					String scopeName = mbd.getScope();
					final Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, () -> {
							beforePrototypeCreation(beanName);
							try {
								return createBean(beanName, mbd, args);
							}
							finally {
								afterPrototypeCreation(beanName);
							}
						});
						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new BeanCreationException(beanName,
								"Scope '" + scopeName + "' is not active for the current thread; consider " +
								"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
								ex);
					}
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}

至此，一个ApplicationContext就启动了起来。并且可以根据应用上下文ApplicationContext获取Bean。