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Spring启动的流程

public class Test {public static void main(String[] args) {ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");Student bean = context.getBean(Student.class);context.close();}
}

调用本类的构造方法

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)throws BeansException {// 调用父类构造方法，进行相关的对象创建等操作,包含属性的赋值操作super(parent);//设置应用程序上下文的配置路径setConfigLocations(configLocations);if (refresh) {refresh();}}

这个refresh方法包含了spring的启动核心流程

public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// Prepare this context for refreshing./*** 做容器刷新前的准备工作* 1、设置容器的启动时间* 2、获取Environment对象，并加载当前系统的属性值到Environment对象中* 3、准备监听器和事件的集合对象，默认为空的集合*/prepareRefresh();// Tell the subclass to refresh the internal bean factory.// 创建容器对象：DefaultListableBeanFactory// 加载xml配置文件的属性值到当前工厂中，最重要的就是BeanDefinitionConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// Prepare the bean factory for use in this context.// beanFactory的准备工作，对各种属性进行填充prepareBeanFactory(beanFactory);try {// Allows post-processing of the bean factory in context subclasses.// 子类覆盖方法做额外的处理，此处我们自己一般不做任何扩展工作，但是可以查看web中的代码，是有具体实现的postProcessBeanFactory(beanFactory);// Invoke factory processors registered as beans in the context.// 调用各种beanFactory处理器invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.// 注册bean处理器，这里只是注册功能，真正调用的是getBean方法registerBeanPostProcessors(beanFactory);// Initialize message source for this context.// 为上下文初始化message源，即不同语言的消息体，国际化处理,在springmvc的时候通过国际化的代码重点讲initMessageSource();// Initialize event multicaster for this context.// 初始化事件监听多路广播器initApplicationEventMulticaster();// Initialize other special beans in specific context subclasses.// 留给子类来初始化其他的beanonRefresh();// Check for listener beans and register them.// 在所有注册的bean中查找listener bean,注册到消息广播器中registerListeners();// Instantiate all remaining (non-lazy-init) singletons.// 初始化剩下的单实例（非懒加载的）finishBeanFactoryInitialization(beanFactory);// Last step: publish corresponding event.// 完成刷新过程，通知生命周期处理器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);}// Destroy already created singletons to avoid dangling resources.// 为防止bean资源占用，在异常处理中，销毁已经在前面过程中生成的单件beandestroyBeans();// 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...resetCommonCaches();}}}

下面挨个讲解上面的13个方法
1.prepareRefresh ，容器启动之前的准备工作

• 设置容器的启动时间
• 获取Environment对象，并加载当前系统的属性值到Environment对象中
• 准备监听器和事件的集合对象，默认为空的集合

protected void prepareRefresh() {// Switch to active.// 设置容器启动的时间this.startupDate = System.currentTimeMillis();// 容器的关闭标志位this.closed.set(false);// 容器的激活标志位this.active.set(true);// 记录日志if (logger.isDebugEnabled()) {if (logger.isTraceEnabled()) {logger.trace("Refreshing " + this);}else {logger.debug("Refreshing " + getDisplayName());}}// Initialize any placeholder property sources in the context environment.// 留给子类覆盖，初始化属性资源initPropertySources();// Validate that all properties marked as required are resolvable:// see ConfigurablePropertyResolver#setRequiredProperties// 创建并获取环境对象，验证需要的属性文件是否都已经放入环境中getEnvironment().validateRequiredProperties();// Store pre-refresh ApplicationListeners...// 判断刷新前的应用程序监听器集合是否为空，如果为空，则将监听器添加到此集合中if (this.earlyApplicationListeners == null) {this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);}else {// Reset local application listeners to pre-refresh state.// 如果不等于空，则清空集合元素对象this.applicationListeners.clear();this.applicationListeners.addAll(this.earlyApplicationListeners);}// Allow for the collection of early ApplicationEvents,// to be published once the multicaster is available...// 创建刷新前的监听事件集合this.earlyApplicationEvents = new LinkedHashSet<>();}

2.obtainFreshBeanFactory 创建容器对象：DefaultListableBeanFactory；加载xml配置文件的属性值到当前工厂中，最重要的就是BeanDefinition

	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {// 初始化BeanFactory,并进行XML文件读取，并将得到的BeanFactory记录在当前实体的属性中refreshBeanFactory();// 返回当前实体的beanFactory属性return getBeanFactory();}

protected final void refreshBeanFactory() throws BeansException {// 如果存在beanFactory，则销毁beanFactoryif (hasBeanFactory()) {destroyBeans();closeBeanFactory();}try {// 创建DefaultListableBeanFactory对象DefaultListableBeanFactory beanFactory = createBeanFactory();// 为了序列化指定id，可以从id反序列化到beanFactory对象beanFactory.setSerializationId(getId());// 定制beanFactory，设置相关属性，包括是否允许覆盖同名称的不同定义的对象以及循环依赖customizeBeanFactory(beanFactory);// 初始化documentReader,并进行XML文件读取及解析,默认命名空间的解析，自定义标签的解析loadBeanDefinitions(beanFactory);this.beanFactory = beanFactory;}catch (IOException ex) {throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);}}

这里创建了DefaultListableBeanFactory容器对象，他能枚举出所有的bean实例

	protected DefaultListableBeanFactory createBeanFactory() {return new DefaultListableBeanFactory(getInternalParentBeanFactory());}

基于xml形式的bean定义读取

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {// Create a new XmlBeanDefinitionReader for the given BeanFactory.// 创建一个xml的beanDefinitionReader，并通过回调设置到beanFactory中XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);// Configure the bean definition reader with this context's// resource loading environment.// 给reader对象设置环境对象beanDefinitionReader.setEnvironment(this.getEnvironment());beanDefinitionReader.setResourceLoader(this);beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));// Allow a subclass to provide custom initialization of the reader,// then proceed with actually loading the bean definitions.//  初始化beanDefinitionReader对象，此处设置配置文件是否要进行验证initBeanDefinitionReader(beanDefinitionReader);// 开始完成beanDefinition的加载loadBeanDefinitions(beanDefinitionReader);}
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {// 以Resource的方式获得配置文件的资源位置Resource[] configResources = getConfigResources();if (configResources != null) {reader.loadBeanDefinitions(configResources);}// 以String的形式获得配置文件的位置String[] configLocations = getConfigLocations();if (configLocations != null) {reader.loadBeanDefinitions(configLocations);}}

类图如下

3.prepareBeanFactory，beanFactory的准备工作，对各种属性进行填充

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {// Tell the internal bean factory to use the context's class loader etc.// 设置beanFactory的classloader为当前context的classloaderbeanFactory.setBeanClassLoader(getClassLoader());// 设置beanfactory的表达式语言处理器beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));// 为beanFactory增加一个默认的propertyEditor，这个主要是对bean的属性等设置管理的一个工具类beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));// Configure the bean factory with context callbacks.// 添加beanPostProcessor,ApplicationContextAwareProcessor此类用来完成某些Aware对象的注入beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));// 设置要忽略自动装配的接口，很多同学理解不了为什么此处要对这些接口进行忽略，原因非常简单，这些接口的实现是由容器通过set方法进行注入的，// 所以在使用autowire进行注入的时候需要将这些接口进行忽略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 interface not registered as resolvable type in a plain factory.// MessageSource registered (and found for autowiring) as a bean.// 设置几个自动装配的特殊规则,当在进行ioc初始化的如果有多个实现，那么就使用指定的对象进行注入beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);beanFactory.registerResolvableDependency(ResourceLoader.class, this);beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);beanFactory.registerResolvableDependency(ApplicationContext.class, this);// Register early post-processor for detecting inner beans as ApplicationListeners.// 注册BPPbeanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));// Detect a LoadTimeWeaver and prepare for weaving, if found.// 增加对AspectJ的支持，在java中织入分为三种方式，分为编译器织入，类加载器织入，运行期织入，编译器织入是指在java编译器，采用特殊的编译器，将切面织入到java类中，// 而类加载期织入则指通过特殊的类加载器，在类字节码加载到JVM时，织入切面，运行期织入则是采用cglib和jdk进行切面的织入// aspectj提供了两种织入方式，第一种是通过特殊编译器，在编译器，将aspectj语言编写的切面类织入到java类中，第二种是类加载期织入，就是下面的load time weaving，此处后续讲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()));}// Register default environment beans.// 注册默认的系统环境bean到一级缓存中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());}}