Spring-MVC: What are a “context” and “namespace”?

Question

From XmlWebApplicationContext javadoc:

By default, the configuration will be taken from \"/WEB-INF/applicationContext.xml\" for the root context, and

Answer 1

"Spring context" = a Spring ApplicationContext.

"root context", in terms of a web application, means the main context that's loaded and used by the webapp. Typically, you'll start the root context with a ContextLoaderListener.

The root context isn't really a "kind" of context. It's just a role that a context plays. You have one root context in a webapp. Other contexts are not the root context. They're usually children of the root context.

A namespace here refers to the scope of an instance of Spring's DispatcherServlet. All it's saying right there is that if you name your servlet "test" in your web.xml, then by convention, Spring will look for a file named "test-servlet.xml" to use as that dispatcher's context. Incidentally, each context like this which is created for a dispatcher becomes a child of the root context.

Edit: To answer your new questions:

1. Follow the link in the first line of my answer to learn about the ApplicationContext. If you have questions not answered there, I'd suggest posting a new SO question.
2. The root context is optional. If you don't have the ContextLoaderListener defined, then you just don't have a root context. When you use a DispatcherServlet, it starts its own ApplicationContext, and it will get the beans it needs from there.
3. I don't know of one off the top of my head. I suppose if there were a need for drastically different configurations between some of the URL resources in your app, that might drive you to do it.
4. Yes. To state it in the proper terms, the root context is the parent context of any context started for a DispatcherServlet. Beans in a parent context are accessible through and by the child context, but the reverse isn't true.