Front Controller - Core J2EE design patterns

Front Controller pattern tells that, “There should be a Single entry and exit point for each and every request made by the user on a single application expecting for a single type of result and the same single controller may interact with different systems or programs to build the response for the request”.


For a better manageability of an application use a Front Controller as the initial point of contact for handling all related requests. The Front Controller centralizes control logic that might otherwise be duplicated, and manages the key request handling activities.


The Front Controller pattern suggests centralizing the handling of all requests but, it does not limit the number of handlers in the system, as does a Singleton. An application may use multiple controllers in a system, each mapping to a set of distinct services

Most of the current MVC based frameworks are using the Front Controller design pattern internally to handle the request from the multiple users.

• Action Servlet is the Front controller in the Struts Framework (1.x)
• Faces Servlet is the Front Controller in the JSF Framework.

Advantages:

Centralizes The Control: It works like a central place to handle system services and business logic across multiple requests and manages business logic processing and request handling. Centralized access to an application means that requests are easily tracked and logged.

Improves Manageability: Front Controller centralizes control, providing a choke point for illicit access attempts into the Web application. In addition, auditing a single entrance into the application requires fewer resources than distributing security checks across all pages.

Improves Reusability: Front Controller promotes cleaner application partitioning and encourages reuse, as code that is common among components moves into a controller or is managed by a controller.

Separates the System Processing Logic: Front Servlet seperates the System Processing logic from view and provides the better manageability from the same.