源码步骤:
//1.先传入一个bean的xml文件
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");

//2.这个xml配置文件,根据它来创建ioc容器
public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
    this(new String[] {configLocation}, true, null);
}

//3.ioc容器底层还要刷新容器
if (refresh) {
    refresh(); 
}

//4.刷新容器的时候。它得先创建bean的工厂
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

//5.创建bean工厂的时候(也叫刷新工厂)
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    refreshBeanFactory();
    return getBeanFactory();
  }

//6.//加载所有的bean定义信息
DefaultListableBeanFactory beanFactory = createBeanFactory(); //创建保存所有bean定义信息的档案馆
      beanFactory.setSerializationId(getId());
      customizeBeanFactory(beanFactory);
      loadBeanDefinitions(beanFactory); 
      this.beanFactory = beanFactory;


//7.beanDefinitionReader去读取传入的xml配置文件的内容()
loadBeanDefinitions(beanDefinitionReader);


//8.读取指定的配置文件
if (configLocations != null) {
  //读取器来加载所有的bean定义信息,也就是相当于读取器从这一行开始去读取配置文件了
  reader.loadBeanDefinitions(configLocations);  
  }

//9.读取器挨个遍历每一个指定的配置文件去来解析
count += loadBeanDefinitions(location);

//10.加载指定配置文件的所有内容
@Override  
public int loadBeanDefinitions(String location) throws BeanDefinitionStoreException {
  return loadBeanDefinitions(location, null);  //加载bean的定义信息,(参数一:配置文件传过来即可)
  }

//11.利用DocumentReader开始读取整篇文档
public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
    BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    int countBefore = getRegistry().getBeanDefinitionCount();
    documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    return getRegistry().getBeanDefinitionCount() - countBefore;
  }

//12.处理bean的定义信息
parseBeanDefinitions(root, this.delegate);

//13.dom解析当前标签生成BeanDefinitionHolder
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
    String id = ele.getAttribute(ID_ATTRIBUTE);
    String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);

//14.准备创建一个抽象的bean定义信息
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);

//15.bean定义信息的类名就是xml配置文件指定写的类名
GenericBeanDefinition bd = new GenericBeanDefinition();  
  bd.setParentName(parentName);
  if (className != null) {
    if (classLoader != null) {
      bd.setBeanClass(ClassUtils.forName(className, classLoader));
      }