Spring源码阅读：XmlWebApplicationContext

XmlWebApplicationContext是spring在web应用中的applicationContext,
在ContextLoaderListener或ContextLoaderServlet中完成了初步的设置。

XmlWebApplicationContext跟其他的applicationContext（FileSystem，Classpath）一样，是AbstractApplicationContext的一个子类。
applicationContext的refresh过程是线程同步的。
如下：
synchronized (this.startupShutdownMonitor)

阅读笔记：

方法1
prepareRefresh();  //设定起始时间，并设置active标记

方法2
prepareBeanFactory(beanFactory);

// 完成BeanFactory的创建

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (logger.isDebugEnabled()) {
            logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
        }
        return beanFactory;
    }

refreshBeanFactory 在AbstractRefreshableApplicationContext（是XmlWebApplicationContext的父类）中进行了实现。
创建了DefaultListableBeanFactory,随后执行loadBeanDefinitions(beanFactory)。
具体的加载过程是委托给XmlBeanDefinitionReader完成。

protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

// Configure the bean definition reader with this context's
// resource loading environment.
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.
initBeanDefinitionReader(beanDefinitionReader);
        loadBeanDefinitions(beanDefinitionReader);
}

该方法中的XmlBeanDefinitionReader完成了WEB-INF/applicationContext.xml(可指定contextConfigLoaction的值，可使用,; \t\n指定多个applicationContext.xml文件)的加载

// 获取beanDefinitionConfig，循环加载

protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
                // 完成所有applicationContext.xml的加载
                reader.loadBeanDefinitions(configLocation);
}
}
}

方法3
下面的一大片，慢慢看吧。

        beanFactory.setBeanClassLoader(getClassLoader());
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver());
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));

// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);

// Initialize message source for this context.
initMessageSource();

// Initialize event multicaster for this context.
initApplicationEventMulticaster();

// Initialize other special beans in specific context subclasses.
onRefresh();

// Check for listener beans and register them.
registerListeners();

// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);

// Last step: publish corresponding event.
finishRefresh();