HomeApache Page 4 - The Properties of Tapestry Pages
Configuring a property in page specification - Apache
In the previous part of this tutorial we started to build a new project, GuessTheWord. The project is very simple, but we are going to spend a lot of time working on it and experimenting with it. This is because the main aim is to learn a lot about the most basic concepts of Tapestry. For every important concept, I want to show you a number of options as to how it can be implemented and explain which option is good for what.
There is yet another way to configure a page property that you might find useful in some cases. Say you want to have a property, but you are not going to read or set the value of that property in your Java code, in the page class. This can happen when the property is going to be used exclusively by some components on the page, so it can be wired to those components within the page specification without writing any Java code at all.
All you need to do is define the property in the page specification:
And then you can reference this property in the bindings of your components, exactly as we do now in the secretWord component binding.
Having found this <property> element in the page specification, Tapestry will act exactly as it does when we’ve provided an abstract getter method: it will create a private property, public getter and setter and will also reset the property to its default value before sending the page to its pool.
All right, but what exactly is this “default value"? According to the rules of Java, any object, including String, will be set to null, while any numeric variable will be sent to zero. But what if you want to have an initial value different from the default one? Say in the GuessTheWord application you want the text box to be not empty, but to display some prompt when the Home page is initially shown to a user.