This question will help gauge a candidate's understanding of a fundamental concept of the current J2EE API, the servlet context. A good understanding of the context path is required for all JSP development, and thus this question is appropriate for both beginners and expert developers alike.

What is the servlet context, and how does it affect the design of JSP pages, servlets, and HTML?

When a J2EE web application is deployed, it is assigned a context path by its container. The context path is the root URL path of the application on the server. All requests targeted at the application's root URL will be passed to the application in question. Within the application, all paths are assumed to be relative to the context path. This allows the application to be deployed on any path deemed appropriate by the container or deployment manager.

This context path assumption applies only to calls into the servlet API however. It is the responsibility of the web developer to assure that any URL references external to the API are made relative to the appropriate context path. This includes anchor tags (links) in an HTML page as well as references to images, style sheets, applets and other content. While hard coding the context path into the HTML will work, a good developer will recognize that this practice will limit the flexibility of deployment for the application, and is undesirable. The scriptlet (or an equivalent custom tag) should be used dynamically prepend the appropriate context path to any URL references. Some servlet containers will provide the mappings for you at run-time, all be it with a decrease in performance. It is important to note that the context path does not include the protocol, port number, or name of the web server. Thus an application accessible at the URL http://www.example.com/myapp has a context path of simply /myapp, not the entire URL.

About the author

Duane Fields is a Java developer, author, and Internet technologist with nearly a decade of professional experience in the design and development of leading edge Internet products and services. Duane is also a respected member of the Java development community and is frequently invited to speak at industry conferences and events. He has co-authored two books and published numerous articles on many aspects of web application development from Java to Relational Databases. The newly expanded, second edition of his best selling book "Web Development with JavaServer Pages" was released in December of 2001.