How to close a Spring ApplicationContext

I've just finished reading chapter 2 Getting Started of Pro Spring 5. Nice and smooth introduction to Spring, and to Dependency Injection motivation.

Going through the provided examples, I had just a minor on the code provided. In a couple of cases, the created Spring contexts is stored in plain ApplicationContexts reference. This is normally considered a good way of writing code. We don't want to bring around a fat interface when a slimmer one would be enough. Anyway, ApplicationContext has no close() method declared, leading to an annoying warning "Resource leak: 'ctx' is never closed".

Here is one place where you could see the issue, in class HelloWorldSpringDI:

ApplicationContext ctx =
    new ClassPathXmlApplicationContext("spring/app-context.xml");

MessageRenderer mr = ctx.getBean("renderer", MessageRenderer.class);
mr.render();

An obvious solution would be explicitly cast ctx to ClassPathXmlApplicationContext, and call close() on it. However, we could do better than that. The Spring application contexts close()'s come from the interface Closeable. This means that we could refactor our code wrapping the ApplicationContext usage in a try-with-resource block. We let Java taking care of calling close() when the context goes out of scope.

The resulting code is something like that:

try (ClassPathXmlApplicationContext ctx =
        new ClassPathXmlApplicationContext("spring/app-context.xml")) {
    MessageRenderer mr = ctx.getBean("renderer", MessageRenderer.class);
    mr.render();
}

I pushed on GitHub my patched code for both HelloWorldSpringDI and HelloWorldSpringAnnotated, that is, the other class suffering for the same lack of application context closing.