Spring源码阅读——ApplicationContext

た入场券 2022-05-18 22:55 231阅读 0赞

Spring中提供了一个接口ApplicationContext，用于扩展BeanFactory中现有的功能。它提供了更多的功能。现在我们来看下它的实现：

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

其中refresh();方法几乎包含了所有的功能，逻辑非常清晰

public void refresh() throws BeansException, IllegalStateException {
            synchronized (this.startupShutdownMonitor) {
                // Prepare this context for refreshing.
                //环境准备，比如系统属性、环境变量的初始化及验证
                prepareRefresh();
    
                // Tell the subclass to refresh the internal bean factory.
                //初始化BeanFactory
                ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
                // Prepare the bean factory for use in this context.
                //对BeanFactory进行各种功能填充
                prepareBeanFactory(beanFactory);
    
                try {
                    // Allows post-processing of the bean factory in context subclasses.
                    //子类覆盖方法做额外处理
                    postProcessBeanFactory(beanFactory);
    
                    // Invoke factory processors registered as beans in the context.
                    //激活各种BeanFactory处理器
                    invokeBeanFactoryPostProcessors(beanFactory);
    
                    // Register bean processors that intercept bean creation.
                    //注册拦截Bean创建的Bean处理器，这里只是注册，真正地调用在getBean的时候，比如配置文件通过${}读取等
                    registerBeanPostProcessors(beanFactory);
    
                    // Initialize message source for this context.
                    //为上下文初始化Message源，（比如国际化处理）
                    initMessageSource();
    
                    // Initialize event multicaster for this context.
                    //初始化应用消息广播，并放入 applicationEventMulticaster bean中
                    initApplicationEventMulticaster();
    
                    // Initialize other special beans in specific context subclasses.
                    //留给子类来初始化其它的bean
                    onRefresh();
    
                    // Check for listener beans and register them.
                    //在所有注册的bean中查找Listener bean，注册到消息广播器中
                    registerListeners();
    
                    // Instantiate all remaining (non-lazy-init) singletons.
                    //初始化剩下的单实例
                    finishBeanFactoryInitialization(beanFactory);
    
                    //完成刷新过程，通知生命周期护处理器lifecycleProcessor刷新过程，同时发出ContextRefreshEvent通知别人（LifecycleProcessor 用来与所有声明的bean的周期做状态更新）
                    // Last step: publish corresponding event.
                    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();
                }
            }
        }