How correctly close the ApplicationContext in Spring?

On the documentation I can read that: usually not possible to call context.close() because many applications (web applications) run indefinitely But what exactly means this last assertion? why web application run indefinitely?

A web application will run as long as the application server that deploys it runs. It is up to the application server (and not to you) to correctly start and stop your application. This means that when the application server is stopped, the servlet context is destroyed. In a Spring application, the ContextLoaderListener class registered in web.xml listens to this event (context destroyed) to properly close the Spring context.

When using Spring outside of an application server (like a standalone application), it is up to you to correctly stop the Spring context. As you said, this can be done by explicitly calling context.close() or registering a shutdown hook (context.registerShutdownHook()) that makes this call for you.

As you are aware that ContextLoaderListener is the one that takes care of initializing and destroying your ApplicationContext, when you shutdown your server, that ContextLoaderListener's contextDestroyed method is invoked.

  public void contextDestroyed(ServletContextEvent event){
    closeWebApplicationContext(event.getServletContext());
    ContextCleanupListener.cleanupAttributes(event.getServletContext());
  }

In that closeWebApplicationContext, they actually call the close method on ApplicationContext like this

  if ((this.context instanceof ConfigurableWebApplicationContext)) {
    ((ConfigurableWebApplicationContext)this.context).close();
  }

This is straight from spring-web-4.1.5.jar. As it is evident from here, they use close to destroy ApplicationContext in web applications.

But registerShutdownHook is used to explicitly shut down IoC container in non-web applications something like a standalone desktop application, specially when you're creating the ApplicationContext manually from ClassPathXmlApplicationContext (or) FileSystemXmlApplicationContext (or) some other types.

This is done to release all resources used by your spring application and to call destroy method on your spring beans if any.