Spring IoC容器的初始化

Spring原始碼分析（一）中提到了很多類，比如BeanDefinition、BeanDefinitionReader、BeanDefintionParser、BeanWrapper等都是ApplicationContext中需要使用的類，都可以從Spring原始碼中的註釋中瞭解

IoC容器的初始化時由前面介紹的AbstractApplicationContext.refresh方法來啟動的，具體來說，這個啟動包括Bean的載入過程和Bean的例項化過程：

• Bean的載入過程分為，BeanDefinition的Resource定位、載入和註冊
• Bean的例項化過程分為，Bean的建立和依賴注入

refresh()原始碼：

    @Override
    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);

            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) {
                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;
            }
        }
    }

Bean載入過程

BeanDefinition的Resource定位

實現路徑：refresh()=>obtainFreshBeanFactory()=>refreshBeanFactory(）=>loadBeanDefinitions()….DefaultResourceLoader.getResource()
這個Resource定位指的是BeanDefinition的資源定位，它由ResourceLoader完成的

BeanDefinition的載入和解析

這個過程是把使用者定義好的Bean表示成IoC容器內部的資料結構，即BeanDefinition
實現路徑：refresh()=>obtainFreshBeanFactory()=>refreshBeanFactory(）=>loadBeanDefinitions()
其中牽扯到很多類，XmlBeanDefinitionReader、BeanDefinitionParserDelegate等等，可以DeBug進去
最後會發現Spring也是用的ClassLoader載入的class檔案，將class資訊封裝成BeanDefinition，也就是之前被註解的類通過讀取class檔案的方式在這被載入（在類ClassPathBeanDefinitionScanner中實現）

BeanDefinition在IoC容器中註冊

實現路徑：refresh()=>obtainFreshBeanFactory()=>refreshBeanFactory(）=>loadBeanDefinitions()……DefaultListableBeanFactory.registerBeanDefinition
最終DeBug的話會調到該方法，哎，只能說Spring好深，DefaultListableBeanFactory繼承了BeanDefinitionRegistry介面，處處可以發現Spring面向介面的程式設計思想，職責分明

    /** Map of bean definition objects, keyed by bean name */
    private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(64);

所有的BeanDefinition都會存放在這個ConcurrentHashMap中

總結

至此Bean的載入過程到此結束，下一章重點分析bean的例項化和依賴注入