spring

spring通过加载配置文件的方式来装载初始化bean。以下面的使用为例：

ApplicationContext ctx = new FileSystemXmlApplicationContext("classpath:performer.xml");Performer performer = (Performer) ctx.getBean("duke");performer.perform();

主要使用到FileSystemXmlApplicationContext，该类的继承结构如下：

AbrstactApplicationContext类做为基本抽象类，实现了大部分方法并且提供了程序基本的运行框架。
在运行过程中，该类的refresh方法会调用obtainFreshBeanFactory方法。通过一步步程序运行定位到
子类AbstractRefreshableApplicationContext中的refreshBeanFactory()方法。
protected final void refreshBeanFactory() throws BeansException {

...DefaultListableBeanFactory beanFactory = createBeanFactory();//初始化beanFactorybeanFactory.setSerializationId(getId());customizeBeanFactory(beanFactory);loadBeanDefinitions(beanFactory);//装载 bean的定义文件  ...

其中loadBeanDefinitions具体是由子类AbstractXmlApplicationContext实现

1 protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {2 // Create a new XmlBeanDefinitionReader for the given BeanFactory.3 XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);// Configure the bean definition reader with this context's// resource loading environment.4 beanDefinitionReader.setEnvironment(this.getEnvironment());5 beanDefinitionReader.setResourceLoader(this);6 beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));// Allow a subclass to provide custom initialization of the reader,// then proceed with actually loading the bean definitions.7 initBeanDefinitionReader(beanDefinitionReader);8 loadBeanDefinitions(beanDefinitionReader);    }

跟踪代码到 类XmlBeanDefinitionReader中 （此时已经获取到配置文件的inputStream流）
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
throws BeanDefinitionStoreException {