Spring容器创建流程（1）容器创建准备

本系列文章将逐一介绍，Spring容器创建到容器刷新完成每个过程。

Spring容器继承结构图

第一步，new容器实例

ApplicationContext factory = new ClassPathXmlApplicationContext("classpath:application.xml");

容器构造器

 public ClassPathXmlApplicationContext(String configLocation) throws BeansException {// 配置路径转为String数组，刷新容器，父容器为nullthis(new String[] {configLocation}, true, null);}

最终调用的构造器

 public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)throws BeansException {super(parent);// 检测解析一下配置文件，保存配置文件路径在 this.configLocations 属性中setConfigLocations(configLocations);if (refresh) {// 容器启动的关键步骤，刷新容器refresh();}}

refresh（）

refresh()方法中完成Spring容器的初始化，事件的派发，bean生命周期管理。是容器创建最重要的一个步骤。方法的实现在AbstractApplicationContext中，这个系列将逐个方法的介绍。

refresh方法概览：可直接跳过。

     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();}}

prepareRefresh();

refresh（）中的第一个方法调用，prepareRefresh，做刷新容器前的准备工作。
废话不说，直接看源码。

 protected void prepareRefresh() {// 设置容器启动时间this.startupDate = System.currentTimeMillis();// 设置容器激活标记this.closed.set(false);this.active.set(true);if (logger.isInfoEnabled()) {logger.info("Refreshing " + this);}// 留给子类initPropertySources();// 获取运行环境，验证属性getEnvironment().validateRequiredProperties();// 创建一个链表存放容器早期事件this.earlyApplicationEvents = new LinkedHashSet<>();}

getEnvironment()

getEnvironment最终获取一个StandardEnvironment。

 @Overridepublic ConfigurableEnvironment getEnvironment() {if (this.environment == null) {this.environment = createEnvironment();}return this.environment;}protected ConfigurableEnvironment createEnvironment() {return new StandardEnvironment();}

StandardEnvironment类型结构

Environment接口代表当前应用所处环境，springBean支持和一个Profile绑定，方便与测试环境开发环境切换。

PropertyResolver中的Property指程序运行时的参数，如系统参数，JVM参数等

StandardEnvironment构造器中做了些什么

// 在构造器中，初始化一些定制属性public AbstractEnvironment() {// 方法在StandardEnvironment中实现// this.propertySources是一个MutablePropertySources用于保存属性customizePropertySources(this.propertySources);if (logger.isDebugEnabled()) {logger.debug("Initialized " + getClass().getSimpleName() + " with PropertySources " + this.propertySources);}}

在StandardEnvironment中实现了定制属性方法

 @Overrideprotected void customizePropertySources(MutablePropertySources propertySources) {     // 添加系统属性propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));// 添加系统环境propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));}

validateRequiredProperties 验证属性

getEnvironment（）得到一个StandardEnvironment，然后调用它父类的的ValidateRequiredProperties进行属性验证。

 @Overridepublic void validateRequiredProperties() throws MissingRequiredPropertiesException {this.propertyResolver.validateRequiredProperties();}
// AbstractEnvironment的解析器
private final ConfigurablePropertyResolver propertyResolver =new PropertySourcesPropertyResolver(this.propertySources);// 在StandarEnvironment父类AbstractEnvironment中@Overridepublic void validateRequiredProperties() throws MissingRequiredPropertiesException {this.propertyResolver.validateRequiredProperties();}@Overridepublic void validateRequiredProperties() {MissingRequiredPropertiesException ex = new MissingRequiredPropertiesException();// 验证是否缺少属性值for (String key : this.requiredProperties) {if (this.getProperty(key) == null) {ex.addMissingRequiredProperty(key);}}if (!ex.getMissingRequiredProperties().isEmpty()) {throw ex;}}