【3】BeanFactory 和AppliactionContext区别

BeanFactory ：是spring框架的基础设施，面向spring本身。会延迟加载，只是将xml解析，将类里面的信息记录下来。
AppliactionContext：应用上下文，面向spring开发者。加载就一次性实例化。

 AppliactionContext 是 extends BeanFactory
代码层次：
一、立即实例化
ApplicationContext ac = new ClassPathXmlApplicationContext("jdbcconfig/springjdbc/springjdbc.xml");

在new的时候 通过构造方法就直接调用了 AbstractApplicationContext里面的 refresh()方法
public void refresh() throws BeansException, IllegalStateException { 
  synchronized (this.startupShutdownMonitor) {
   // Prepare this context for refreshing.
   prepareRefresh();

   // Tell the subclass to refresh the internal bean factory.
   ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

   // Prepare the bean factory for use in this context.
   prepareBeanFactory(beanFactory);//开始实例化类了会调用 AbstractBeanFactory 的 doGetBean（）方法。

   try {
    // 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();
   }

   catch (BeansException ex) {
    // Destroy already created singletons to avoid dangling resources.
    destroyBeans();

    // Reset 'active' flag.
    cancelRefresh(ex);

    // Propagate exception to caller.
    throw ex;
   }
  }
 }

二、延迟实例化
XmlBeanFactory bf = new XmlBeanFactory(res);
构造方法里面 相等于调用了  AbstractApplicationContext里面的 refresh()方法里面的obtainFreshBeanFactory（）
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

XmlWebApplicationContext==》AbstractRefreshableApplicationContext ==》 AbstractApplicationContext 父类
 loadBeanDefinitions()方法                        refreshBeanFactory()方法实现类               refreshBeanFactory()抽象方法、 refresh()方法 
                                                                      getBeanFactory（）实现类

实例化过程
ac.getBean();

AbstractApplicationContext类里面的
public Object getBean(String name) throws BeansException {
  assertBeanFactoryActive();
  return getBeanFactory().getBean(name);
 }

AbstractRefreshableApplicationContext
 public final ConfigurableListableBeanFactory getBeanFactory() {
  synchronized (this.beanFactoryMonitor) {
   if (this.beanFactory == null) {
    throw new IllegalStateException("BeanFactory not initialized or already closed - " +
      "call 'refresh' before accessing beans via the ApplicationContext");
   }
   return this.beanFactory;
  }
 }

AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory
AbstractBeanFactory//
 public Object getBean(String name) throws BeansException {
  return doGetBean(name, null, null, false);
 }

protected <T> T doGetBean()方法里面的
Object sharedInstance = getSingleton(beanName);//获取实例化，如果已经实例化了，就不用再实例化了

sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {//这个是创建Create bean instance.

Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(64);//实例化的对象放在这里面

xbf.getBean();
 T doGetBean(
   final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)方法