AbstractApplicationContext的refresh方法是提纲挈领的一个方法。这个方法如果全部读懂了，基本上Spring的源码就Over完了。下面先贴上refresh的方法源码

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            prepareRefresh();
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            prepareBeanFactory(beanFactory);
            try {
                postProcessBeanFactory(beanFactory);
                invokeBeanFactoryPostProcessors(beanFactory);
                registerBeanPostProcessors(beanFactory);
                initMessageSource();
                initApplicationEventMulticaster();
                onRefresh();
                registerListeners();
                finishBeanFactoryInitialization(beanFactory);
                finishRefresh();
            }
            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization -cancelling refresh attempt: " + ex);
                }
                destroyBeans();
                cancelRefresh(ex);
                throw ex;
            }
            finally {
                resetCommonCaches();
            }
        }
    }

下面开始仔细分析各种方法的功能：
1.prepareRefresh

protected void prepareRefresh() {
        this.startupDate = System.currentTimeMillis();
        this.closed.set(false);
        this.active.set(true);

        if (logger.isDebugEnabled()) {
            if (logger.isTraceEnabled()) {
                logger.trace("Refreshing " + this);
            }
            else {
                logger.debug("Refreshing " + getDisplayName());
            }
        }

        // Initialize any placeholder property sources in the context environment
        initPropertySources();

        // Validate that all properties marked as required are resolvable
        // see ConfigurablePropertyResolver#setRequiredProperties
        getEnvironment().validateRequiredProperties();

        // Allow for the collection of early ApplicationEvents,
        // to be published once the multicaster is available...
        this.earlyApplicationEvents = new LinkedHashSet<>();
    }

功能：做一些刷新之前的准备工作。例如：设置下active和closed标志；记录下refresh开始的时间.或者是初始化一下property属性配置信息的资源(这个在Web方面用到了,会初始化servletConfig信息).
下面的那句：getEnvironment().validateRequiredProperties()会对上面的initPropertySources()初始化的信息进行验证工作，具体的验证逻辑，我也没看，所以，暂且放这儿不说，以后专门补充写这个细节。
2.obtainFreshBeanFactory

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        refreshBeanFactory();
        return getBeanFactory();
    }

功能：刷新Bean的工程，然后获取到Bean的工厂。原先我以为是就是重新new一个BeanFactory，结果不是那么简单，原来XML的解析，生成BeanDefinition，之后load进去都是在这个方法做的。所以这个需要专门做一个文章来解释。
未完待续，先贴上再说