JavaServer Pages, 3rd Edition

Using Servlets and JSP

The combination of servlets and JSP is a powerful tool for developing well-structured applications that are easy to maintain and extend as new requirements surface. Since a servlet is a regular Java class, you can use the full power of the Java language to implement the request processing, using standard Java development and debugging tools. JSP pages can then be used for what they are best at: rendering the response by including information collected or generated by the servlets.

A common combination of servlets and JSP is to use one servlet as the Controller (or front component, as it’s called in the J2EE documents) for an application, with a number of JSP pages acting as Views. This approach lets you develop the application in a more modular fashion, with the servlet acting as a gateway, dispatching requests to specialized processing components and picking the appropriate JSP page for the response based on success or failure.

Prior to the 2.3 version of the servlet specification, servlets were often used to also make sure that application policies were applied for all requests. For instance, with application-controlled authentication and access control, centralizing the security controls in a servlet instead of counting on everyone remembering to put custom actions in all protected pages was less error-prone. Using a servlet as the single entry point to the application also made it easier to do application-specific logging (for instance collect statistics ...