The Action returns an ActionForward
When the Action completes, it returns an ActionForward. If the ActionForward is null, the ActionServlet assumes the response has been generated and does nothing. Otherwise, the ActionServlet reads the ActionForward and either redirects or forwards the request as appropriate.
If the request is another Action URI, the container will return the request to the ActionServlet. Otherwise, the container sends the request to another servlet or service. If the ActionForward is set for redirect, the request is sent back to the client with instructions to submit a new request to the specified location.
Jasper (or equivalent) renders a JavaServer Page
When the ActionServlet sends a request to a JSP, the request is handled by another service, such as Jasper. Typically, the Struts and other tag extensions are used to write the dynamic portions of the page. Sometimes a JSP template may be used so that the page is built up from other components. Most often, the dynamic data is passed to the page in the request context in a JavaBean. This is known as the View Helper pattern [Go3]. The tag extensions simply call methods on the JavaBeans that return the formatted data. How data is positioned on a page is considered part of the presentation logic. The format of the data itself is usually part of the business logic, so it is delegated to the bean. The Struts tags may also access view helpers provided by the framework. These include localized labels and prompts, error messages, and hyperlink paths. In addition, Struts tags can evaluate expressions, iterate through lists, and populate the controls in an HTML form.
Another servlet renders the response
After processing an Action, the request can be sent to any other servlet or service in the application. Other presentation systems, such as Velocity templates, can access framework resources through the servlet contexts.
Summary
Today’s developers need to build full-featured applications that can be maintained over time. Web application frameworks such as Struts solve common problems, so developers can focus on their application’s unique functionality. Frameworks are especially important when building web applications since the way HTTP and HTML work makes
creating dynamic applications difficult.
Struts makes the most of the standard Java servlet API and has even become an informal compliance test for servlet containers. Struts also builds on the common design patterns, especially the MVC architectural paradigm. The framework encourages a “layered” design for applications. This design helps make applications both robust and scalable. A key part of the Struts architecture is the way it extends the flow of the base HTTP request-response cycle. The Struts controller manages the paths used by your application, helps to safely collect input from users, and can localize application messages— especially error messages. Struts is a performant solution. It will not hold your application back and usually frees resources that can be better used elsewhere. Of course, Struts has its flaws. Many of the classnames were hastily chosen during development and can be confusing; other areas could also be improved. Despite any drawback, Struts is easily the most popular web application framework available today.
April 12, 2007
Struts