spring-core-3-29 | Spring IoC容器生命周期：IoC容器启停过程中发生了什么？

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Spring IoC 容器生命周期

• 启动
• 运行
• 停止
代码示例

/** Licensed to the Apache Software Foundation (ASF) under one or more* contributor license agreements.  See the NOTICE file distributed with* this work for additional information regarding copyright ownership.* The ASF licenses this file to You under the Apache License, Version 2.0* (the "License"); you may not use this file except in compliance with* the License.  You may obtain a copy of the License at**     http://www.apache.org/licenses/LICENSE-2.0** Unless required by applicable law or agreed to in writing, software* distributed under the License is distributed on an "AS IS" BASIS,* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.* See the License for the specific language governing permissions and* limitations under the License.*/
package org.geekbang.thinking.in.spring.ioc.overview.container;import org.geekbang.thinking.in.spring.ioc.overview.domain.User;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;import java.util.Map;/*** 29 | Spring IoC容器生命周期：IoC容器启停过程中发生了什么?* 只是一个大概介绍* @author <a href="mailto:mercyblitz@gmail.com">Mercy</a>* @since*/
@Configuration
public class AnnotationApplicationContextAsIoCContainerDemo {public static void main(String[] args) {// 创建 BeanFactory 容器AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();// 将当前类 AnnotationApplicationContextAsIoCContainerDemo 作为配置类（Configuration Class）applicationContext.register(AnnotationApplicationContextAsIoCContainerDemo.class);// 启动应用上下文applicationContext.refresh();/*applicationContext的refresh()方法就是以前针对spring启动过程分析的核心方法, 这里只是简单一讲,点进去看看实现:@Overridepublic void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {// synchronized 这里加锁是因为applicationContext可以在程序的任何位置创建,而spring 的设计者并不知道你会不会多线程创建什么的, 当然要加锁// Prepare this context for refreshing. 看下面讲解prepareRefresh();// Tell the subclass to refresh the internal bean factory.// 这里去刷新一个内部的beanFactory, 而且是用子类来实现// 有两种可能, 一种是空实现, 一种是抽象实现, 看下面讲解ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();// Prepare the bean factory for use in this context.// 这里面会有一大堆操作,// 里面有两个方法涉及到前面我们讲的内建的 bean的注入和非bean(依赖)注入// beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());// beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);// 后面这里也会有详细讲解prepareBeanFactory(beanFactory);try {// Allows post-processing of the bean factory in context subclasses.// 这个方法就是一个BeanFactory的扩展点, 可以自己对BeanFactory(容器)进行API的扩展postProcessBeanFactory(beanFactory);// Invoke factory processors registered as beans in the context.// 上面调整完了这里执行invokeBeanFactoryPostProcessors(beanFactory);// Register bean processors that intercept bean creation.// 这个方法则是对Bean进行调整, 就是对注入的用户定义的bean的调整// 这里只是注册, 具体的调用是在BeanFactory中进行的registerBeanPostProcessors(beanFactory);// Initialize message source for this context.// 国际化的初始initMessageSource();// Initialize event multicaster for this context.// 应用事件的广播initApplicationEventMulticaster();// Initialize other special beans in specific context subclasses.onRefresh();// Check for listener beans and register them.// 注册监听器registerListeners();// Instantiate all remaining (non-lazy-init) singletons.// 上下文注册的一个结束流程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();}}}protected void prepareRefresh() {// Switch to active. 记录一下启动的时间, 那么就可以记录初始化总共用了多少时间之类的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.// 后面在 Environment抽象里面会讲到这一部分initPropertySources();// Validate that all properties marked as required are resolvable:// see ConfigurablePropertyResolver#setRequiredProperties// 与校验相关的一个部分getEnvironment().validateRequiredProperties();// Store pre-refresh ApplicationListeners...// earlyApplicationListeners会在spring的事件中进行分析, 这个场景比较复杂if (this.earlyApplicationListeners == null) {this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);}else {// Reset local application listeners to pre-refresh state.this.applicationListeners.clear();this.applicationListeners.addAll(this.earlyApplicationListeners);}// Allow for the collection of early ApplicationEvents,// to be published once the multicaster is available...this.earlyApplicationEvents = new LinkedHashSet<>();}protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {// 看得出来这里提供的是一个不完整的实现, 下面两个方法都是抽象实现.// refreshBeanFactory有一个常见的实现就是// org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory, 看后面refreshBeanFactory();return getBeanFactory();// 特别注意一定, 玩游戏看颜色, 学技术看版本// 我们分析用的是5.2.2.RELEASE版本, 如果低于或高于这个版本, 这里看到的代码都不一样// 如果用的是SNAPSHOT版本, 源码可能会随之覆盖和更新, 因此一定要用RELEASE版本或MILESTONE版本}@Overrideprotected final void refreshBeanFactory() throws BeansException {// 如果存在BeanFactory就先销毁if (hasBeanFactory()) {destroyBeans();closeBeanFactory();}try {// 之前看过的, 创建一个DefaultListableBeanFactory,// 这是个组合, 同时与ApplicationContext不是一个对象DefaultListableBeanFactory beanFactory = createBeanFactory();beanFactory.setSerializationId(getId());customizeBeanFactory(beanFactory);// 读取bean的定义loadBeanDefinitions(beanFactory);// 这里有把锁, 同样也是因为refreshBeanFactory可以外部调用, 不是主线程调用的,// 加了锁防止线程不安全synchronized (this.beanFactoryMonitor) {this.beanFactory = beanFactory;}}catch (IOException ex) {throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);}}至于资源的操作其实是靠继承的父类来完成的: DefaultResourceLoaderpublic abstract class AbstractApplicationContext extends DefaultResourceLoaderimplements ConfigurableApplicationContext// 在web容器中的调用会复杂一些, 如tomcat等, 在springBoot中会有一些嵌套,// 但最终还是要走上面那一套流程*/// 依赖查找集合对象lookupCollectionByType(applicationContext);applicationContext.close();/*关闭应用上下文public void close() {// 关闭要相对比较简单synchronized (this.startupShutdownMonitor) {doClose();// If we registered a JVM shutdown hook, we don't need it anymore now:// We've already explicitly closed the context.if (this.shutdownHook != null) {try {Runtime.getRuntime().removeShutdownHook(this.shutdownHook);}catch (IllegalStateException ex) {// ignore - VM is already shutting down}}}}protected void doClose() {// Check whether an actual close attempt is necessary...if (this.active.get() && this.closed.compareAndSet(false, true)) {if (logger.isDebugEnabled()) {logger.debug("Closing " + this);}LiveBeansView.unregisterApplicationContext(this);try {// Publish shutdown event.publishEvent(new ContextClosedEvent(this));}catch (Throwable ex) {logger.warn("Exception thrown from ApplicationListener handling ContextClosedEvent", ex);}// Stop all Lifecycle beans, to avoid delays during individual destruction.if (this.lifecycleProcessor != null) {try {this.lifecycleProcessor.onClose();}catch (Throwable ex) {logger.warn("Exception thrown from LifecycleProcessor on context close", ex);}}// Destroy all cached singletons in the context's BeanFactory.// 可以销毁所有的beandestroyBeans();// Close the state of this context itself.// 关闭掉BeanFactorycloseBeanFactory();// Let subclasses do some final clean-up if they wish...// 这个方法可以自定义, 实现自己需要的关闭方法onClose();// Reset local application listeners to pre-refresh state.if (this.earlyApplicationListeners != null) {this.applicationListeners.clear();this.applicationListeners.addAll(this.earlyApplicationListeners);}// Switch to inactive.this.active.set(false);}}*/}/*** 通过 Java 注解的方式，定义了一个 Bean* 相当于用 Java 代码 进行配置*/@Beanpublic User user() {User user = new User();user.setId(1L);user.setName("小马哥");return user;}private static void lookupCollectionByType(BeanFactory beanFactory) {if (beanFactory instanceof ListableBeanFactory) {ListableBeanFactory listableBeanFactory = (ListableBeanFactory) beanFactory;Map<String, User> users = listableBeanFactory.getBeansOfType(User.class);System.out.println("查找到的所有的 User 集合对象：" + users);}}}