Spring在初始化过程中要做的事情很多，下面我们就根据ClassPathXmlApplicationContext初始化看看我们的应用走了哪些步骤，我用debug模式下一步步来展现初始化过程。
首先我们看一下ClassPathXmlApplicationContext类的继承关系
ClassPathXmlApplicationContext
AbstractXmlApplicationContext
AbstractRefreshableConfigApplicationContext
AbstractRefreshableApplicationContext
AbstractApplicationContext
DefaultResourceLoader
I ResourceLoad
ApplicationContext context = new ClassPathXmlApplicationContext("conf/applicationContext.xml");
public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent)
throws BeansException {
super(parent);
setConfigLocations(configLocations);
if (refresh) {
refresh();
}
}
初始化应用上下文，使用ClassPathXmlApplicationContext类新建实例，初始化这个类，我们可以看到使用super方法初始化了父类，上面继承树中所有的类都初始化了；然后把传送的配置文件目录设置为配置文件；调用refresh方法，这个方法是AbstractApplicationContext类实现的方法。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
//准备上下文的刷新，
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
//得到新的Bean工厂，应用上下文加载bean就是在这里面实现的
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//准备bean工厂用在上下文中
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
//允许子类上下问处理bean工厂
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
//请求工厂处理器作为beans注册在上下文
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
//注册bean处理器拦截bean创建
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
//初始化上下文中消息源
initMessageSource();
// Initialize event multicaster for this context.
//初始化上下文中事件广播
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
//初始化其他具体bean
onRefresh();
// Check for listener beans and register them.
//检查监听bean并注册
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
//实例化未初始化单例
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
//最后一步发布相应事件
finishRefresh();
}
obtainFreshBeanFactory方法把配置文件中的bean加载到容器中。调用AbstractRefreshableApplicationContext的refreshBeanFactory方法，然后调用loadBeanDefinitioans(beanFactory)方法，这个方法的实现类是XmlWebApplicationContext的loadBeanDefinitions方法，方法调用Reader中的loadBeanDefinitions(configLocations)把配置文件传入Reader。
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//这里定义了Reader来读取Bean，在loadBeanDifinitions方法中传入reader
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
......
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}
XmlBeanDefinitionReader中调用AbstractBeanDefinition中的loadBeanDefinitions(location)方法。把配置文件读取成Resource后，调用XmlBeanDefinitionReader中loadBeanDefinitions(Resource)方法，在方法中调用doLoadBeanDefinitions(InputSource inputSource, Resource resource)传入参数是文件流和Resource，方法内调用registerBeanDefinitions(Document doc,Resource resource)方法
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
documentReader.setEnvironment(this.getEnvironment());
int countBefore = getRegistry().getBeanDefinitionCount();
documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
return getRegistry().getBeanDefinitionCount() - countBefore;
}
在DocumentReader调用注册bean方法中进行注册，调用DefaultBeanDefinitionDocumentReader的doRegisterBeanDefinitions方法，在parseBeanDefinitions方法中调用parseDefaultElement(ele, delegate);方法，判断如果获取到的是个bean的话执行，processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate)方法最后在DefaultListableBeanFactory类中调用registerBeanDefinition进行注册，注册的容器是this.beanDefinitionMap.put(beanName, beanDefinition);，这个是初始化的CurrentHashMap类。
容器的初始化以及Bean的注册就完成了。
