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My First Application

The Wicket application we are going to develop is the ubiquitous Hello, World! application. Simply put, we will create a web page using Wicket technology for printing the Hello, World! string on a web page.
In the second release, some interactivity will be added to show how to do simple form related component development.

The goal is to generate the following markup:

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The HTML

Even though the requested result is so simple, there are many ways to achieve it. In this example we will use a rendering component called 'Label' to create the text 'Hello, World!'. So basically we have two things to consider:

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The markup for the HTML page is the same as earlier:

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It is of course possible to add header information, apply style sheets, put javascript in there, etc. For the sake of the example, this is omitted.

Using this HTML-code is cheating, since we don't generate the required string programatically, but have hard coded it in the HTML page.
In order to have Wicket render the text through a component, we need to tell Wicket which piece of the web page is a component. In this case we can replace the text with a label component definition.

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We have used the span element to markup the component and the wicket:id attribute to identify the component.

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First we need to create a web page. Wicket has a WebPage class suited for this task. All webpages need to be subclasses of WebPage. Another requirement is that the actual HTML file and the class name are equal: Index.html and Index, IndexPage.html and IndexPage or HelloWorld.html and HelloWorld. They also need to be in the same place on the classpath. The best way to develop is to put them in the same directory. This might seem strange in the beginning, especially when you are accustomed to separate html files and java files. However, since all pages are actually just components, it makes perfect sense in terms of reusability.

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Note that the base package names changed or rather moved from Wicket version 1.3. This means that if you are using these versions you would need to change your imports (and other references to these for packages/classes) to reflect these new package locations. The basic idea is just to prefix all your wicket packages with "org.apache". For example, the imports:

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would change to:

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When you add components, you need to give them an identifier in the form of a string. In the above example, our component's identifier is 'message'. The id should be unique within it's own scope. In other words, no siblings are allowed with the same id.

When the markup is rendered, the id's of tags are matched against the component ids. Thus

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will look for a component with the id 'message' in the current scope.

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Our application could look like this:

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Sidenote: To see changes to template files immediately, include the following snippet in your web.xml or to use a system property -Dwicket.configuration

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web.xml configuration

To load our application and have it available, we need to add the following lines to web.xml:

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And you are now ready to run your first Wicket app!

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If you wish to build the package manually, you would need the following directory structure.

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Then to build the application, make sure wicket-1.3.0.jar is in your classpath, and build the .java files. To run you need to ensure all .jar files in the "lib" directory are in your classpath. For most web servers and servlet containers (Tomcat for one) will automatically load all these files in the lib directory into your classpath.

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