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Which components shall we need? - Apache

In the previous article, you witnessed the interplay between a Tapestry page and its components (granted, we had only one simple component there, but you get my point). Page class, when rendering its page, finds any components mentioned in the template and asks those components to display themselves, as they know better how to do that. Components, in their turn, might need some information to display themselves, and they ask the page class to provide the necessary information by calling some of its methods.

TABLE OF CONTENTS:
  1. Introducing Simple Components in Apache Tapestry
  2. What is OGNL?
  3. Implicit vs. declared components
  4. GuessTheWord project
  5. Creating mock ups
  6. Which components shall we need?
By: Alexander Kolesnikov
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April 23, 2007

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Now letís think about which components we are going to need on these two pages.

First of all, the text box for entering a secret word should obviously be a component as the page class will need to know which word was entered by the user. Page class will have a property to store the entered word. Imagine: the HTML page produced by the page class and sent to the user on the one hand, and the server where the page class lives on the other hand can be thousands of miles apart. And still, there is some sort of data connection between Tapestry components on the page and the corresponding properties of the page class.

When the HTML page is rendered for the first time to be shown to the user, Tapestry components will display the initial values of the properties connected to them. When the user has filled in the form and submitted it, the page class will receive the new values and put them into the properties in place of the initial values.

But, yes, to send new values to the server, some form should be submitted. So the text box component, to work properly, should be surrounded by a form component. Right now, we have an HTML form on the page mock up, so we need only to make it a Tapestry component.

All in all, we need two components for the Home page.

The Secret page is very simple; all its text is hard-coded. However, we shall need to define whether the secret word was guessed properly, and if it was, show the greeting. This is one component, a conditional one. If the word was wrong however, we need to display an alternative message. You will see that Tapestry employs for this purpose yet another component.

Finally, the link leading back to the Home page should be a component too. This is because in Tapestry you donít need to know URLs corresponding to different pages and use them to create links. You only need to tell the framework which page you want to see when the link is clicked, and there is a simple component intended exactly for this purpose.

Having an idea now of what kind of functionality we are going to need on our pages, we can go to the Tapestry 4.1 website (http://tapestry.apache.org/tapestry4.1/) and check which components are available there.

We shall find that, quite conveniently, Tapestry has a TextField component for displaying text boxes. There is also a Form component to contain the TextField. Naturally, the component named If will check if some condition is true and show or hide accordingly anything surrounded by this component. There is also a component named Else that should be placed after an If component. It will show its contents when the condition of the If component evaluates to false. Finally, there is a PageLink component, and its purpose is to provide a link to another page of the Web application.

You see, Tapestry provides everything we need. In the next article, we will configure the components on the pages.



 
 
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