Java(TM) Boutique - Strictly Struts

Tutorials : Strictly Struts :

Designing Action components

One of the limitations of Struts is that one JSP can be associated with only one form bean at one point of time. Similarly, one Action class can map to one form bean per configuration. Note that you can configure the same Action class with different path names mapping to different form beans. Because of such limitations (Is it really a limitation?) situations like following may become tricky to handle.

Let us think that our Student registration case study now involves a Teacher to be associated with a Student. So a Student is related to a Teacher and vice-versa. We declare two separate form beans for Student and Teacher and also two separate Action classes, StudentAction and TeacherAction, handling Student and Teacher separately. Now you might want to display the associated Teacher information from a Student page and also you may want to do the same in reverse. The problem here is that the StudentAction class maps only to Student form bean. In the JSP, where you display the Student, information has a link to the Teacher object. But in order to display the teacher information, you need to forward the application to the Teacher JSP page which maps to the Teacher form bean. However, StudentAction class has mapping to Student form bean only and you have no way to populate the Teacher form bean from within the StudentAction class.

In order to tackle such situations, it is a good idea to create Action components. For example, you might create a separate Action class solely to display the Teacher information. This Action class will also map to the Teacher form bean. The pre- condition for this Action class will be that you either pass the Teacher object to be displayed as part of the request or session object and the display Action class then pick that up and populate the corresponding form bean, forwarding the application to the Teacher JSP page which can then display the teacher information set in the form bean.

When you click the Teacher link from the Student JSP page, you definitely call the StudentAction class (as that is what is mapped as the form submit). Within the Student Action class you detect that you want to display the Teacher information and then CHAIN the action to the TeacherDisplayAction class by setting the Teacher object as part of the request or session object. The following diagram will make things clearer.

You can achieve the Action chaining simply through the configuration file. Here is a sample:

 
<action    path="/studentAction"
               type="StudentAction"
               name="studentForm"
               parameter="methodToCall"
               scope="request"
               validate="true"
               input="/student.jsp">
       <forward name="displayTeacher"              path="/displayTeacher.do"/>
    </action>
 
<action    path="/ displayTeacher "
               type="DisplayTeacherAction"
               name="teacherForm"
               scope="request">
       <forward name="success"              path="/teacher.jsp"/>
    </action>

Notice that the Action chaining is merely forwarding the application to a different action.

The DisplayTeacherAction class body might look like the following:

public class DisplayTeacherAction extends Action
{
 
    public ActionForward execute(ActionMapping mapping, ActionForm form, 
HttpServletRequest req, HttpServletResponse res) throws Exception
{
     //get the Teacher object from the request
    Teacher teacher = (Teacher)req.getAttribute(“teacher”);
 
   //populate the teacher form bean with the Teacher data
   
    //forward the application to display teacher
   return mapping.findForward(“success”);
   }
}

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