Java(TM) Boutique - Coding your second Jakarta Struts Application

Tutorials : Coding your second Jakarta Struts Application :

The DetailForm bean

This bean is actually straightforward. You may see the complete code here. Two things may be noted:

1. The "validate" method checks if the "id" and "title" field have been filled in:

// Check if Id and Title are present 
ActionErrors errors = new ActionErrors();
if (id == null || id.equals("")) {
  errors.add("id", new ActionError("error.id.missing"));
}  
if (title == null || title.equals("")) {
  errors.add("title", new ActionError("error.title.missing"));
}  
return errors;

This is just to show an example of validation. In a real application you'd probably also want to check if the "id" for a "create" was already in use.

2. Since "update" and "create" both need to get the actors in an ArrayList, I've added some code in "validate" that does precisely this.

The Action classes

Since most of the hard work is done in the DVDManager bean, the Action classes are rather short. This is something you should always strive for--to keep your Action classes small. The Action classes should be considered part of the controller (the "C" in "MVC") and should therefore act as relays or adapters to the business logic.

Let's have a look on some of the more interesting Action classes. You'll find a link to them all in the Resources section at the end of the article.

The ListDVDAction class

This is the first of our classes that is being called. The first time it is called it'll build an instance of the DVDManager bean that holds the DVDs as a List of JDOM Elements. This bean is saved in the user's session.

  public ActionForward perform(ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response) {

    HttpSession session = request.getSession();
    DVDManager dvds = (DVDManager)session.getAttribute("dvds");
    if (dvds == null) {
      // Get the name of the xml file from the config file 
      String filename = mapping.getParameter();
      session.setAttribute("filename",filename);
      
      // Read the XML file and save it in a bean
      dvds = new DVDManager();
      dvds.buildDocument(filename);
      
      // Save the bean in session scope 
      session.setAttribute("dvds",dvds);
      System.out.println
	   ("Reading dvds.xml: " + dvds.getNumberOfDvds());
    }  

    // Forward control to the list page
    return (mapping.findForward("list"));
  }

The DetailDVDAction class

This class is rather typical. First you get the index of the DVD from the form bean. Then you retrieve the DVDManager bean, and using the index value, you now copy the data from this bean to the form bean. Note that I've sketched some simple error handling. The "error.nodvds" key is looked up in the ApplicationResources.properties file by the error.jsp page.

  public ActionForward perform(ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response) {

    // Get the index of the DVD (given in the hyperlink)  
    DetailForm df = (DetailForm)form;
    String index = df.getIndex();
    int ix = Integer.parseInt(index);
    
    // Get the bean with dvd info
    HttpSession session = request.getSession();
    DVDManager dvds = (DVDManager)session.getAttribute("dvds");
    if (dvds == null) {
      request.setAttribute("errormessage","error.nodvds");
      return (mapping.findForward("error"));
    }  
    
    // Transfer the data from the dvd bean to the ActionForm
    dvds.setIndex(ix);
    df.setId(dvds.getId());
    df.setTitle(dvds.getTitle());
    df.setLength(dvds.getLength());
    df.setActors(dvds.getActorLines());

    // Forward control to the detail page 
    return (mapping.findForward("detail"));
  }

The CreateDVDAction class

Again: get the data from the form bean, get the DVD bean, use it's create method.

  public ActionForward perform(ActionMapping mapping,
    ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response) {

    // Get the data from the Form bean
    DetailForm df = (DetailForm)form;       
    String id = df.getId();
    String title = df.getTitle();
    String length = df.getLength();
    ArrayList actorsList = df.getActorsList();
    
    // Get the bean with dvd info
    HttpSession session = request.getSession();
    DVDManager dvds = (DVDManager)session.getAttribute("dvds");
    
    // Create a new DVD
    dvds.createDVD(id, title, length, actorsList);

    // Forward control to the next page
    return (mapping.findForward("OK"));
  }

In the config file "OK" points to the Detail page, and is therefore easily changed to the List page if you prefer.

Applet Index
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