<servlet><servlet-name>spring-mvc</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring-mvc.xml</param-value></init-param><load-on-startup>1</load-on-startup>
</servlet>

https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html

For many applications, having a single WebApplicationContext is simple and suffices. It is also possible to have a context hierarchy where one root WebApplicationContext is shared across multiple DispatcherServlet (or other Servlet) instances, each with its own child WebApplicationContext configuration. See Additional Capabilities of the ApplicationContext for more on the context hierarchy feature.The root WebApplicationContext typically contains infrastructure beans, such as data repositories and business services that need to be shared across multiple Servlet instances.
Those beans are effectively inherited and can be overridden (that is, re-declared) in the Servlet-specific child WebApplicationContext, which typically contains beans local to the given Servlet.

@Override
public final void init() throws ServletException {// 1.读取init parameters 等参数，其中就包括设置contextConfigLocation PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);//2.初始化servlet中使用的beaninitServletBean();
}

Override
protected final void initServletBean() throws ServletException {//初始化webApplicationContextthis.webApplicationContext = initWebApplicationContext();
}
protected WebApplicationContext initWebApplicationContext() {//1.获得rootWebApplicationContextWebApplicationContext rootContext =WebApplicationContextUtils.getWebApplicationContext(getServletContext());WebApplicationContext wac = null;//2.如果还没有webApplicatioinContext，创建webApplicationContextif (wac == null) {//创建webApplicationContextwac = createWebApplicationContext(rootContext);}return wac;
}

public static WebApplicationContext getWebApplicationContext(ServletContext sc) {return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
}public static WebApplicationContext getWebApplicationContext(ServletContext sc, String attrName) {Object attr = sc.getAttribute(attrName);return (WebApplicationContext) attr;
}

protected WebApplicationContext createWebApplicationContext(WebApplicationContext parent) {return createWebApplicationContext((ApplicationContext) parent);
}
createWebApplicationContext(ApplicationContext parent) {//1.获取WebApplicationContext实现类，此处其实就是XmlWebApplicationContextClass<?> contextClass = getContextClass();//生成XmlWebApplicationContext实例ConfigurableWebApplicationContext wac =(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);//2.设置rootWebApplicationContext为父容器 wac.setParent(parent);//3.设置配置文件wac.setConfigLocation(getContextConfigLocation());//4.配置webApplicationContext.configureAndRefreshWebApplicationContext(wac);return wac;
}
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {//开始处理beanwac.refresh();
}

protected <T> T doGetBean(// 获取父BeanFactoryBeanFactory parentBeanFactory = getParentBeanFactory();//如果父容器不为空，且本容器没有注册此bean就去父容器中获取beanif (parentBeanFactory != null && !containsBeanDefinition(beanName)) {// 如果父容器有该bean，则调用父beanFactory的方法获得该beanreturn (T) parentBeanFactory.getBean(nameToLookup,args);}//如果子容器注册了bean，执行一系列实例化bean操作后返回bean.//此处省略实例化过程.....return (T) bean;
}

<context:component-scan base-package="xx.xx.xx"/>