11.2.2、创建WebApplicationContext

所在类：org.springframework.web.servlet.FrameworkServlet

protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
    Class<?> contextClass = getContextClass();
    if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { 
        throw new ApplicationContextException( "Fatal initialization error in servlet with name '" + 
                                              getServletName() + 
                                              "': custom WebApplicationContext class [" + contextClass.getName() 
                                              + "] is not of type ConfigurableWebApplicationContext"); 
    }
    // 通过反射创建 IOC 容器对象 
    ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    wac.setEnvironment(getEnvironment()); 
    // 
    设置父容器 wac.setParent(parent);
    String configLocation = getContextConfigLocation();
    if (configLocation != null) {
        wac.setConfigLocation(configLocation);
    }
    configureAndRefreshWebApplicationContext(wac); 
    return wac; 
}