Hello World</>
<para>
In this first example, we'll create a very simple "Hello World" kind of application. It won't have
any real functionality but it'll demonstrate the simplest possible variation of a number of key
aspects of the framework.
</>
<para>
We'll define our application, define the lone page of our application, configure everything and
launch it.
</>
<para>
The code for this section of the tutorial is in the Java package <classname>tutorial.hello</>, i.e.,
<filename class=directory>C:\Tapestry-<replaceable>x.x.x</>\Examples\Tutorial\tutorial\hello</>.
</>
<section id="hello.engine">
<title>Application Engine</>
<para>
As each new client connects to the application, an instance of the application engine is created for
them. The application engine is used to track that client's activity within the application.
</>
<para>
The application engine is an instance, or subclass of, the Tapestry class
<classname>com.primix.tapestry.engine.SimpleEngine</>.
</>
<para>
In these first few examples, we have no additional behavior to add to the provided base class, so
we simply use <classname>SimpleEngine</> directly.
</>
</section>
<section id="hello.servlet">
<title>Application Servlet</>
<para>
The application servlet is a "bridge" between the servlet container and the application engine. Its
job is simply to create (on the first request) or locate (on subsequent requests) the application
engine.
</>
<para>
The application servlet must subclass
<classname>com.primix.tapestry.ApplicationServlet</> and
implement the method: <function>getApplicationSpecificationPath()</>.
This method provides the
path to the application specification file; the servlet reads this file when it is initialized.
</>
<figure>
<title>HelloWorldServlet.java</>
<programlisting>package tutorial.hello;
import com.primix.tapestry.*;
public class HelloWorldServlet extends ApplicationServlet
{
protected String getApplicationSpecificationPath()
{
return "/tutorial/hello/HelloWorld.application";
}
}</programlisting></figure>
</section>
<section id="hello.appspec">
<title>Application Specification</>
<para>
The application specification is used to describe the application to the Tapestry framework. It
provides the application with a name, an engine class, and a list of pages.
</>
<para>
This specification is a file that is located on the Java class path. In a deployed Tapestry
application, the specification lives with the application's class files, in the
<filename class=directory>WEB-INF/classes</> directory of a War file.
</>
<figure>
<title>HelloWorld.application</>
<programlisting><![CDATA[<?xml version="1.0"?>
<!DOCTYPE application PUBLIC "-//Primix Solutions//Tapestry Specification 1.0//EN"
"http://tapestry.sourceforge.net/dtd/Tapestry_1_0.dtd">
<application>
<name>Hello World Tutorial</name>
<engine-class>com.primix.tapestry.engine.SimpleEngine</engine-class>
<page>
<name>Home</name>
<specification-path>/tutorial/hello/Home.jwc</specification-path>
</page>
</application>]]></programlisting></figure>
<para>
Our application is very simple; we give the application a name, use the standard engine, and define
a single page, named "Home". In Tapestry, components are specified with the path to their
specification file (a file that end with '.jwc').
</>
<para>
Page "Home" has a special meaning to Tapestry: when you first launch a Tapestry application, it
loads and displays the "Home" page. All Tapestry applications are required to have such a home
page.
</>
</section>
<section id="hello.home-page-spec">
<title>Home Page Specification</>
<para>
The page specification defines the Tapestry component responsible for the page. In this first
example, our component is very simple.
</>
<figure>
<title>Home.jwc</>
<programlisting><![CDATA[<?xml version="1.0"?>
<!DOCTYPE specification PUBLIC
"-//Primix Solutions//Tapestry Specification 1.0//EN"
"http://tapestry.sourceforge.net/dtd/Tapestry_1_0.dtd">
<specification>
<class>com.primix.tapestry.BasePage</class>
</specification>]]></programlisting></figure>
<para>
This simply says that <varname>Home</> is a kind of page. We use the supplied Tapestry class
<classname>com.primix.tapestry.BasePage</> since we aren't adding any behavior to the page.
</>
</section>
<section id="hello.home-page-template">
<title>Home Page Template</>
<para>
Finally, we get to the content of our application. This file is also a Java resource;
it isn't directly
visible to the web server. It has the same location and name as the component specification,
except that it ends in "html".
</>
<figure>
<title>Home.html</>
<programlisting><![CDATA[<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Hello World
Welcome to your first Tapestry Application.