Struts Action Classes

The Action class defines two methods that could be executed depending on your servlet environment:

public ActionForward execute(ActionMapping mapping,

                    ActionForm form,

                    ServletRequest request,

                    ServletResponse response)

                    throws Exception;

 

public ActionForward execute(ActionMapping mapping,

                    ActionForm form,

                    HttpServletRequest request,

                    HttpServletResponse response)

                    throws Exception;

Since the majority of teams using the framework are focused on building web applications, most projects will only use the "HttpServletRequest" version. A non-HTTP execute() method has been provided for applications that are not specifically geared towards the HTTP protocol.

The goal of an Action class is to process a request, via its execute method, and return an ActionForward object that identifies where control should be forwarded (e.g. a JSP, Tile definition, Velocity template, or another Action) to provide the appropriate response. In the MVC/Model 2 design pattern, a typical Action class will often implement logic like the following in its execute method:

• Validate the current state of the user's session (for example, checking that the user has successfully logged on). If the Action class finds that no logon exists, the request can be forwarded to the presentation page that displays the username and password prompts for logging on. This could occur because a user tried to enter an application "in the middle" (say, from a bookmark), or because the session has timed out, and the servlet container created a new one.
• If validation is not complete, validate the form bean properties as needed. If a problem is found, store the appropriate error message keys as a request attribute, and forward control back to the input form so that the errors can be corrected.
• Perform the processing required to deal with this request (such as saving a row into a database). This can be done by logic code embedded within the Action class itself, but should generally be performed by calling an appropriate method of a business logic bean.
• Update the server-side objects that will be used to create the next page of the user interface (typically request scope or session scope beans, depending on how long you need to keep these items available).
• Return an appropriate ActionForward object that identifies the presentation page to be used to generate this response, based on the newly updated beans. Typically, you will acquire a reference to such an object by calling findForward on either the ActionMapping object you received (if you are using a logical name local to this mapping), or on the controller servlet itself (if you are using a logical name global to the application).