public interface HandlerInterceptor {  
    /**
    * 预处理回调方法，实现处理器的预处理（如登录检查），第三个参数为响应的处理器（如我们上一章的Controller实现）
    * 返回值：true表示继续流程（如调用下一个拦截器或处理器）；
    * false表示流程中断（如登录检查失败），不会继续调用其他的拦截器或处理器，此时我们需要通过response来产生响应
    */
    boolean preHandle(  
            HttpServletRequest request, HttpServletResponse response,   
            Object handler)   
            throws Exception;  
    /**
    * 后处理回调方法，实现处理器的后处理（但在渲染视图之前），此时我们可以通过modelAndView（模型和视图对象）对模型数据进行处理或对视图进行处理，modelAndView也可能为null。
    */
    void postHandle(  
            HttpServletRequest request, HttpServletResponse response,   
            Object handler, ModelAndView modelAndView)   
            throws Exception;  
    /**
    * 整个请求处理完毕回调方法，即在视图渲染完毕时回调，如性能监控中我们可以在此记录结束时间并输出消耗时间 ，
    * 还可以进行一些资源清理，类似于try-catch-finally中的finally，但仅调用处理器执行链中preHandle返回true的拦截器的afterCompletion。
    */
    void afterCompletion(  
            HttpServletRequest request, HttpServletResponse response,   
            Object handler, Exception ex)  
            throws Exception;  
}   

ApplicationContext ac = new ClassPathXmlApplicationContext("spring.xml");
MyTestBean bean = (MyTestBean)ac.getBean("myTestBean");

   public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, ApplicationContext parent) throws BeansException {
        super(parent);
        this.setConfigLocations(configLocations);
        if (refresh) {
            this.refresh();
        }
    }

    @Override
	public void refresh() throws BeansException, IllegalStateException {
       //方法是加锁的，避免多线程同时刷新Spring上下文
		synchronized (this.startupShutdownMonitor) {
			//准备工作包括设置启动时间，是否激活标识位，初始化属性源(property source)配置
			prepareRefresh();

			//创建beanFactory（过程是根据xml为每个bean生成BeanDefinition并注册到生成的beanFactory）
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			//准备创建好的beanFactory（给beanFactory设置ClassLoader，设置SpEL表达式解析器，设置类型转化器【能将xml String类型转成相应对象】，增加内置ApplicationContextAwareProcessor对象，忽略各种Aware对象，注册各种内置的对账对象【BeanFactory，ApplicationContext】等，注册AOP相关的一些东西，注册环境相关的一些bean
			prepareBeanFactory(beanFactory);

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

				//实例化并调用BeanFactory中扩展了BeanFactoryPostProcessor的Bean的postProcessBeanFactory方法
				invokeBeanFactoryPostProcessors(beanFactory);

				//实例化和注册beanFactory中扩展了BeanPostProcessor的bean
				registerBeanPostProcessors(beanFactory);

				//实例化，注册和设置国际化工具类MessageSource
				initMessageSource();

				//实例化，注册和设置消息广播类（如果没有自己定义使用默认的SimpleApplicationEventMulticaster实现，此广播使用同步的通知方式）
				initApplicationEventMulticaster();

				//设置样式工具ThemeSource
				onRefresh();

				//添加用户定义的消息接收器到上面设置的消息广播ApplicationEventMulticaster
				registerListeners();

				//设置自定义的类型转化器ConversionService，设置自定义AOP相关的类LoadTimeWeaverAware，清除临时的ClassLoader，冻结配置（没看明白干什么的），实例化所有的类（懒加载的类除外）
				finishBeanFactoryInitialization(beanFactory);

				//注册和设置跟bean生命周期相关的类（默认使用DefaultLifecycleProcessor），调用扩展了SmartLifecycle接口的start方法，使用上注册的广播类消息广播类ApplicationEventMulticaster广播ContextRefreshedEvent事件 
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

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

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}

public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException {
    return this.doGetBean(name, requiredType, args, false);
}

protected <T> T doGetBean(String name, Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {
    //提取对应的beanName
    final String beanName = this.transformedBeanName(name);
    /*
     *检查缓存中或者实例工厂中是否有对应的实例
     *为什么首先会使用这段代码呢，因为在创建单例bean的时候会存在依赖注入的情况，而在创建依赖的时候为了避免循环依赖，
     *Spring创建bean的原则是不等bean创建完成就会将创建bean的ObjectFactory提早曝光，
     *也就是将ObjectFactory加入到缓存中，一旦下个bean创建时候需要依赖上个bean则直接使用ObjectFactory
     */
    //直接尝试从缓存获取或者singletonFactories中的ObjectFactory中获取
    Object sharedInstance = this.getSingleton(beanName);
    Object bean;
    if(sharedInstance != null && args == null) {
        if(this.logger.isDebugEnabled()) {
            if(this.isSingletonCurrentlyInCreation(beanName)) {
                this.logger.debug("Returning eagerly cached instance of singleton bean \'" + beanName + "\' that is not fully initialized yet - a consequence of a circular reference");
            } else {
                this.logger.debug("Returning cached instance of singleton bean \'" + beanName + "\'");
            }
        }

        //返回对应的实例，有时候存在诸如BeanFactory的情况并不是直接返回实例本身而是返回指定方法返回的实例
        bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
    } else {
        //只有在单例情况下才会尝试解决循环依赖，原型模式情况下，如果存在
        //A中有B的属性，B中有A的属性，那么当依赖注入的时候，就会产生当A还未创建完的时候因为
        //对于B的创建再次返回创建A，造成循环依赖，也就是下面的情况
        //isPrototypeCurrentlyInCreation(beanName)为true
        if(this.isPrototypeCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }

        BeanFactory parentBeanFactory = this.getParentBeanFactory();
        //如果BeanDefinitionMap中也就是在所有已经加载的类中不包括beanName则尝试从parentBeanFactory中检测
        if(parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
            String var19 = this.originalBeanName(name);
            //递归到BeanFactory中寻找
            if(args != null) {
                return parentBeanFactory.getBean(var19, args);
            }

            return parentBeanFactory.getBean(var19, requiredType);
        }

        //如果不是仅仅做类型检查则是创建bean，这里要进行记录
        if(!typeCheckOnly) {
            this.markBeanAsCreated(beanName);
        }

        //将存储XML配置文件的GernericBeanDefinition转换为RootBeanDefinition，如果指定BeanName是子Bean的话同时会合并父类的相关属性
        final RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
        this.checkMergedBeanDefinition(mbd, beanName, args);
        String[] dependsOn = mbd.getDependsOn();
        String scopeName;
        //若存在依赖则需要递归实例化依赖的bean
        if(dependsOn != null) {
            String[] var14 = dependsOn;
            int ex = dependsOn.length;

            for(int scope = 0; scope < ex; ++scope) {
                scopeName = var14[scope];
                this.getBean(scopeName);
                //缓存依赖调用
                 this.registerDependentBean(scopeName, beanName);
            }
        }

        //实例化依赖的bean后便可以实例化mbd本身了
        //singleton模式的创建
        if(mbd.isSingleton()) {
            sharedInstance = this.getSingleton(beanName, new ObjectFactory() {
                public Object getObject() throws BeansException {
                    try {
                        return AbstractBeanFactory.this.createBean(beanName, mbd, args);
                    } catch (BeansException var2) {
                        AbstractBeanFactory.this.destroySingleton(beanName);
                        throw var2;
                    }
                }
            });
            bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
        } else if(mbd.isPrototype()) {
            //prototype模式的创建(new)
            scopeName = null;

            Object var20;
            try {
                this.beforePrototypeCreation(beanName);
                var20 = this.createBean(beanName, mbd, args);
            } finally {
                this.afterPrototypeCreation(beanName);
            }

            bean = this.getObjectForBeanInstance(var20, name, beanName, mbd);
        } else {
            //指定的scope上实例化bean
            scopeName = mbd.getScope();
            Scope var21 = (Scope)this.scopes.get(scopeName);
            if(var21 == null) {
                throw new IllegalStateException("No Scope registered for scope \'" + scopeName + "\'");
            }

            try {
                Object var22 = var21.get(beanName, new ObjectFactory() {
                    public Object getObject() throws BeansException {
                        AbstractBeanFactory.this.beforePrototypeCreation(beanName);

                        Object var2;
                        try {
                            var2 = AbstractBeanFactory.this.createBean(beanName, mbd, args);
                        } finally {
                            AbstractBeanFactory.this.afterPrototypeCreation(beanName);
                        }

                        return var2;
                    }
                });
                bean = this.getObjectForBeanInstance(var22, name, beanName, mbd);
            } catch (IllegalStateException var18) {
                throw new BeanCreationException(beanName, "Scope \'" + scopeName + "\' is not active for the current thread; " + "consider defining a scoped proxy for this bean if you intend to refer to it from a singleton", var18);
            }
        }
    }

    //检查需要的类型是否符合bean的实际类型
    if(requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
        throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    } else {
        return bean;
    }
}