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ContextLoaderListener类是负责初始化IOC容器，即在我们的web项目中，这里就是IOC容器初始化的入口，由这个类启动IOC容器的初始化。
它配置在web.xml中，比如如下配置：
<context-param><param-name>contextConfigLocation</param-name><param-value>classpath:context/applicationContext.xml</param-value></context-param><!-- Spring监听器 --><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>
跟踪ContextLoaderListener类，可以看到有一个如下方法
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {String configLocationParam;if(ObjectUtils.identityToString(wac).equals(wac.getId())) {configLocationParam = sc.getInitParameter("contextId");if(configLocationParam != null) {wac.setId(configLocationParam);} else {wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(sc.getContextPath()));}}wac.setServletContext(sc);configLocationParam = sc.getInitParameter("contextConfigLocation"); //很显然这里就是读取web.xml中配置的资源文件的路径，也就是上述context-param
标签配置的参数if(configLocationParam != null) {wac.setConfigLocation(configLocationParam);}ConfigurableEnvironment env = wac.getEnvironment();if(env instanceof ConfigurableWebEnvironment) {((ConfigurableWebEnvironment)env).initPropertySources(sc, (ServletConfig)null);}this.customizeContext(sc, wac);wac.refresh(); //有了资源文件后，在这里开启IOC容器的初始化}
refresh方法的实现是在AbstractApplicationContext类中，代码如下：
public void refresh() throws BeansException, IllegalStateException {Object var1 = this.startupShutdownMonitor;synchronized(this.startupShutdownMonitor) {this.prepareRefresh();ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();this.prepareBeanFactory(beanFactory);try {this.postProcessBeanFactory(beanFactory);this.invokeBeanFactoryPostProcessors(beanFactory);this.registerBeanPostProcessors(beanFactory);this.initMessageSource();this.initApplicationEventMulticaster();this.onRefresh();this.registerListeners();this.finishBeanFactoryInitialization(beanFactory);this.finishRefresh();} catch (BeansException var9) {if(this.logger.isWarnEnabled()) {this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);}this.destroyBeans();this.cancelRefresh(var9);throw var9;} finally {this.resetCommonCaches();}}}
上述代码就会进行完整的IOC容器的初始化
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