Struts Dialogs Mail Reader: Subscriptions

Subscriptions component performs the following functions:

• Displays a list of email subscriptions
• Allows to create a new sibscription
• Allows to update existing subscription

Subscriptions component is controlled by one action (SubscriptionAction.java) and has two views: subscriptions.jsp and subscription.jsp.

subscriptions.jsp displays a list of email subscriptions. It is shown to a logged-in user, if there is no current subscription.

If current subscription exists, subscription.jsp displays it to a logged-in user. It can be either a new subscription...

...or an existing subscription:

SubscriptionAction class does not differ much from standard all-in-one CRUD Component. The major difference is that Subscription action first verifies if a user is logged in. If not, it redirects to Login action. If user is logged in, then Subscription action handles input events in standard way for DialogAction class. In real application this code should be placed in an interceptor or servlet filter. Struts Chains, introduced in Struts 1.3, should allow easy implementation of generic interceptors like login interceptor.

 public class SubscriptionAction extends CRUDAction {
   ...
   public ActionForward execute(ActionMapping mapping,
                                ActionForm form,
                                HttpServletRequest request,
                                HttpServletResponse response)
     throws Exception {

     // If user not found, redirect to login action
     HttpSession session = request.getSession();
     if (session.getAttribute(Constants.USER_KEY) == null) {
       return mapping.findForward("logon");
     }

     // User is valid, perform standard event processing
     return super.execute(mapping, form, request, response);
   }
   ...
 }

If current subscription does not exist, Subscrpiptions action displays subscrpiption list. This list can be split into pages. Default page size is four rows. Struts-EL is used to access actionform data.

 <table>
 <thead>
   <tr>
     <th>Host</th>
     <th>Username</th>
     <th>Server Type</th>
     <th >Auto</th>
     <th>Operation</th>
   </tr>
 </thead>

 <logic:present name="user" scope="session">
   <!-- Show subscription list -->
   <logic-el:iterate id="subscription"
                     collection="${SubscriptionForm.subscriptions}"
                     offset="${SubscriptionForm.offset}"
                     length="${SubscriptionForm.pagesize}"
                     type="net.jspcontrols.mailreader.business.Subscription">
     <tr>
       <td><c:out value="${subscription.host}"/></td>
       <td><c:out value="${subscription.username}"/></td>
       <td><c:out value="${subscription.type}"/></td>
       <td><c:out value="${subscription.autoConnect}"/></td>
       <td>
         <html-el:link 
           href="Subscriptions.do?DIALOG-EVENT-UPDATE&host=${subscription.host}">
           Edit
         </html-el:link>
         <html-el:link 
           href="Subscriptions.do?DIALOG-EVENT-DELETE&host=${subscription.host}">
           Delete
         </html-el:link>
       </td>
     </tr>
   </logic-el:iterate>
 </logic:present>
 </table>

 <html:form action="/Subscriptions.do">
   <html:submit property="DIALOG-EVENT-CREATE" value="New Subscription"/> 
   <html-el:submit property="DIALOG-EVENT-PREVPAGE" value="Previous Page" 
                   disabled="${SubscriptionForm.firstpage}"/> 
   <html-el:submit property="DIALOG-EVENT-NEXTPAGE" value="Next Page" 
                   disabled="${SubscriptionForm.lastpage}"/> 
   <html:submit property="DIALOG-EVENT-BACKHOME" value="Cancel"/> 
 </html:form>

The major difference of this version of MailReader application from original Ted Husted's version is that action form has session scope and current subscription is nested within the action form. Fortunately, Subscrption business object (BO) has only String and boolean fields, so no conversion is needed and it is easy to retain invalid values in the form.

When a user creates new subscription, a new Subscription object is created and nested in the SubscriptionForm.java class. If a user wants to update existing subscription, then it is cloned into a detached object, which in turn, is nested within SubscriptionForm.java class. Therefore, changes to nested subscription do not affect persistent data. If the user cancels the update process, then detached subscription is simply deleted from memory.

Subscription action creates new or updates existing subscription based on input event generated by button on subscriptions.jsp page. DIALOG-EVENT-CREATE creates new subscription, DIALOG-EVENT-UPDATE selects a subscription as current and updates it.

Proceed to Registration component.