What Is the Struts Framework?

The Struts Framework is a standard for developing well-architected Web applications. It has the following features:

• Open source
• Based on the Model-View-Controller (MVC) design paradigm, distinctly separating all three levels:
  • Model: application state
  • View: presentation of data (JSP, HTML)
  • Controller: routing of the application flow
• Implements the JSP Model 2 Architecture
• Stores application routing information and request mapping in a single core file, struts-config.xml

The Struts Framework, itself, only fills in the View and Controller layers. The Model layer is left to the developer.

Architecture Overview

All incoming requests are intercepted by the Struts servlet controller. The Struts Configuration file struts-config.xml is used by the controller to determine the routing of the flow. This flows consists of an alternation between two transitions:

From View to Action	A user clicks on a link or submits a form on an HTML or JSP page. The controller receives the request, looks up the mapping for this request, and forwards it to an action. The action in turn calls a Model layer (Business layer) service or function.
From Action to View	After the call to an underlying function or service returns to the action class, the action forwards to a resource in the View layer and a page is displayed in a web browser.

The diagram below describes the flow in more detail:

1. User clicks on a link in an HTML page.
2. Servlet controller receives the request, looks up mapping information in struts-config.xml, and routes to an action.
3. Action makes a call to a Model layer service.
4. Service makes a call to the Data layer (database) and the requested data is returned.
5. Service returns to the action.
6. Action forwards to a View resource (JSP page)
7. Servlet looks up the mapping for the requested resource and forwards to the appropriate JSP page.
8. JSP file is invoked and sent to the browser as HTML.
9. User is presented with a new HTML page in a web browser.

Struts Components

The Controller

This receives all incoming requests. Its primary function is the mapping of a request URI to an action class selecting the proper application module. It's provided by the framework.

The struts-config.xml File

This file contains all of the routing and configuration information for the Struts application. This XML file needs to be in the WEB-INF directory of the application.

Action Classes

It's the developer's responsibility to create these classes. They act as bridges between user-invoked URIs and business services. Actions process a request and return an ActionForward object that identifies the next component to invoke. They're part of the Controller layer, not the Model layer.

View Resources

View resources consist of Java Server Pages, HTML pages, JavaScript and Stylesheet files, Resource bundles, JavaBeans, and Struts JSP tags.

ActionForms

These greatly simplify user form validation by capturing user data from the HTTP request. They act as a "firewall" between forms (Web pages) and the application (actions). These components allow the validation of user input before proceeding to an Action. If the input is invalid, a page with an error can be displayed.

Model Components

The Struts Framework has no built-in support for the Model layer. Struts supports any model components:

• JavaBeans
• EJB
• CORBA
• JDO
• any other

by Exadel