Java Enterprise in a Nutshell, Third Edition

Web Applications

Now that we’ve seen a basic servlet, we can step back for a moment and talk about how servlets are integrated into the servlet container. A web application consists of a set of resources, including servlets, static content, JSP files, and class libraries, installed in a particular path on a web server. This path is called the servlet context, and all servlets installed within the context are given an isolated, protected environment to operate in, without interference from (or the ability to interfere with) other software running on the server.

A servlet context directory tree contains several different types of resources. These include class files and jar files (which aren’t exposed to clients connecting via web browsers), JSP files (which are processed by the JSP servlet before being fed back to the client), and static files, such as HTML documents and JPEG images, which are served directly to the browser by the web server.

The context has a virtual component, too. For each context, the servlet container will instantiate separate copies of servlets and will create a private address space that can be accessed via the ServletContext class. Servlets running in the same context can use this class to communicate with each other. We’ll discuss this more later.

The simplest servlet installations create just a single context, rooted at /, which is the top of the web server path tree. Servlets and static content are installed within this context. Most of the time, you’ll ...