Struts Meaning...

Why we need a controller architecture:
There are two basic architectures for JavaServer Pages (JSP) development. The first is a page-centric design that allows requests to be made directly to a JSP. The problem with this approach is that it will lead to JSPs with excessive embedded Java code.

The second, a Model-View-Controller (MVC) architecture variant often called Model 2, is a controller design that uses servlets to handle requests and JSPs to handle presentation. This allows for easy separation of function. Although this is an improvement over the pure JSP model, this design is not without problems. If we code a separate controller servlet for each page, we can end up with dozens of almost identical servlets. If we code a single controller servlet, we end up with a monolithic class with a huge if/else statement that can be difficult to maintain. What's needed to solve this problem is a controller architecture that can handle the repetitive details while still remaining flexible and easy to maintain.

What is Struts?

Struts is an open source application framework that provides a flexible and easy to use controller architecture. The nature of the framework helps to promote a Model 2 application architecture with clear separation of functionality. Struts includes a controller servlet, JSP custom tag libraries, and utility classes.

Struts is being developed as part of the Jakarta project, sponsored by the Apache Software Foundation. Since it is an open source project, it can be downloaded from http://jakarta.apache.org/struts and used for free.

In this article I will explain the installation of Struts and discuss some of the basic functionality that it provides. For purposes of this discussion, I will be working with Struts installed in Tomcat running on a Win32 platform. To demonstrate some of the functionality of Struts we will code a simple logon function.
The Struts Architecture

Struts provides the controller that will serve as the entry point for all requests into our application. The controller determines which Java class will handle a particular request by referring to an XML file that contains mappings of URL paths to Java classes. For a class to be usable by the Struts controller it must extend the Struts Action class. Struts will call the perform( ) method of the Action object passing it the Servlet request and response objects as well as some Struts objects which we will discuss in more detail later.

In addition, Struts can also be used to run a form pre-processor to do simple form validation. This is controlled through the same XML file. We will also discuss this topic.

Struts also has custom JSP tag libraries that can simplify JSP programming. Besides special functionality used in Struts programming, custom tags can provide commonly used functionality such as iterating through a collection. Since the Apache Project includes the development of common custom tag libraries, the Struts tag libraries may change in the future
web.xml File

There are two XML files that we, as Struts developers, will need to maintain. The first is the web.xml file for our application. This file is stored in the application WEB-INF directory. An example web.xml file is shown in Listing 1.

The first section of this file identifies the Struts controller class, ActionServlet and provides parameters for this class. The "application" parameter identifies a properties file that contains error messages used by the application. The "config" parameter identifies the Struts configuration file (more on this later).

The second section of the web.xml file tells Tomcat when to invoked the ActionServlet. In our example, ActionServlet will be invoked whenever a URL ending with ".do" is found. For example, http://127.0.0.1/struts/login.do will invoke the ActionServlet.

The final section identifies the Struts tag libraries.
Struts Configuration File

Listing 2 shows a simple struts-config.xml file that is passed as a parameter to the ActionServlet. It should be placed in the same directory as the web.xml file. The struts-config.xml file can have several sections. The first section we will look at is the section. tells Struts which class to invoke from the ActionServlet. Only the "path" and "type" are required entries. The "type" tells Struts which Action class to invoke when a URL with the model of the "path" is found. From the example in Listing 2, the URL http://127.0.0.1/struts/login.do will cause the ActionServlet to run a method in the class "LoginAction".

The other tag inside the tag is the tag. This tag gives a way to identify which JSP should be given control by the Action class without coding it inside the class itself.