spring refresh()源码解析

refresh()方法是ApplicationContext接口中定义的方法，它的实现在AbstractApplicationContext抽象类中。

下面是refresh()方法的源码解析：

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) {
            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();
        }
    }
}

refresh()方法主要分为以下几个步骤：

1.调用prepareRefresh()方法，准备刷新应用程序上下文。

2.调用obtainFreshBeanFactory()方法，创建或获取新的BeanFactory。BeanFactory是Spring的Bean容器，它负责管理Bean的生命周期。

3.调用prepareBeanFactory()方法，对BeanFactory进行一些准备工作，例如设置类加载器、添加属性编辑器等。

4.调用postProcessBeanFactory()方法，允许子类在BeanFactory初始化完成后对BeanFactory进行进一步的处理。

5.调用invokeBeanFactoryPostProcessors()方法，对注册在应用程序上下文中的BeanFactoryPostProcessor进行处理。

6.调用registerBeanPostProcessors()方法，注册BeanPostProcessor，这些BeanPostProcessor用于在Bean实例化之后执行一些操作。

7.调用initMessageSource()方法，初始化消息源，用于国际化。

8.调用initApplicationEventMulticaster()方法，初始化事件广播器，用于事件的发布和监听。

9.调用onRefresh()方法，允许子类在应用程序上下文刷新完成后执行一些特殊的操作。

10.调用registerListeners()方法，注册事件监听器。

11.调用finishBeanFactoryInitialization()方法，实例化所有的singleton bean。

12.调用finishRefresh()方法，完成应用程序上下文的刷新。

13.如果在刷新过程中出现异常，会调用destroyBeans()方法销毁已经创建的singleton Bean，然后抛出异常。