Spring 啟動時最重要的方法refresh()，
1. 在obtainFreshBeanFactory();中建立所有物件的BeanDefinition
2. 在finishBeanFactoryInitialization(beanFactory);中建立真正的單例物件,及其依賴物件的繫結

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {

            //呼叫容器準備重新整理的方法，獲取容器的當時時間，同時給容器設定同步標識  
 

            // Prepare this context for refreshing.
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            // 得到所有物件的BeanDefinition
            // 告訴子類啟動refreshBeanFactory()方法，Bean定義資原始檔的載入從  
            // 子類的refreshBeanFactory()方法啟動  
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
                AbstractApplicationContext.refreshBeanFactory();
                AbstractApplicationContext.loadBeanDefinitions(beanFactory);
                AbstractXmlApplicationContext.loadBeanDefinitions(beanDefinitionReader);

            // 為BeanFactory配置容器特性，例如類載入器、事件處理器等  
 

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                // 為容器的某些子類指定特殊的BeanPost事件處理器 
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // 呼叫所有註冊的BeanFactoryPostProcessor的Bean  
 

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // 為BeanFactory註冊BeanPost事件處理器.  
                // BeanPostProcessor是Bean後置處理器，用於監聽容器觸發的事件  
                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);

                // 初始化資訊源，和國際化相關.
                // Initialize message source for this context.
                initMessageSource();

                // 初始化容器事件傳播器.
                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // 呼叫子類的某些特殊Bean初始化方法 
                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // 為事件傳播器註冊事件監聽器
                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                // 初始化容器內所有剩餘的單例物件，物件間的依賴關係也在此維護
                finishBeanFactoryInitialization(beanFactory);
                    beanFactory.preInstantiateSingletons();
                    for (String beanName : beanNames) {
                        getBean(beanName);
                    }

                // 初始化容器的生命週期事件處理器，併發布容器的生命週期事件  
                // 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;
            }
        }
    }