WebStack

Annotated docs/resources.html

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2005-04-24 paulb file changeset files shortlog [project @ 2005-04-24 15:43:10 by paulb] Added a better description of how resources are created, and made the simple example slightly easier to follow. Introduced a separate page for design considerations. Rearranged some of the deployment documentation.
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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  <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type" />
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  <title>Applications and Resources</title>
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 content="amaya 8.1a, see http://www.w3.org/Amaya/" />
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</head>
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<body>
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<h1>Applications and Resources</h1>
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At its simplest a WebStack application is just&nbsp;a single Python
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class that we call a "resource". This class can be defined inside a
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normal Python module or package, so let us start by doing the following:<br />
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<ol>
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  <li>Create a new directory for
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our application; choose any name since we just want an empty space in
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which to put new files.</li>
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  <li>Create a file called <code>MyApplication.py</code>
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- this is our module.</li>
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</ol>
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We are going to call our resource&nbsp;<code>MyResource</code>
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and in principle it will have a structure that looks like this:
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<pre>class MyResource:<br />    def respond(self, trans):<br />        [Examine the transaction, decide what the user wants to do.]<br />        [Perform some kind of action with the information supplied.]<br />        [Produce some kind of response which tells the user what happened.]</pre>
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<p>It is in this kind of resource
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class that we write the
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actual application code or at least the beginnings of it. When a user
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of the application sends us a request,
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the <code>respond</code>&nbsp;method
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will be called and the code
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within it executed. The parts of the pseudo-code in
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the above text which aren't valid Python
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(ie. the bits in square brackets) will, when we have written them, use
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the&nbsp;<code>trans</code>
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object to find out what any given user of the application has sent us,
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and to send information back
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to the
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user in response.</p>
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<h2>Starting Simple</h2>
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<p>The simplest way to turn this
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into a working application is to
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ignore the first two activities mentioned in the pseudo-code and just
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to produce some kind of
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response. Here is how we can make our application do something:</p>
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<ol>
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  <li>Edit the&nbsp;module
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file&nbsp;<code>MyApplication.py</code>.</li>
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  <li>Write into it the following
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code which defines&nbsp;<code>MyResource</code>:</li>
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</ol>
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<pre>class MyResource:<br />   &nbsp;def respond(self, trans):<br />        out = trans.get_response_stream()<br />        print &gt;&gt;out, "Hello world."</pre>
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<h2>Testing the Resource</h2>
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<p>To test this resource we need to deploy it, and to do that we need
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an
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adapter. Here is a quick way of writing an adapter and testing this
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code:</p>
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<ol>
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  <li> Create a&nbsp;file called&nbsp;<code>MyAdapter.py</code> - you
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can choose another name if you want - this will be where the adapter
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code lives.</li>
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  <li>Copy the example adapter in <a href="deploying.html">"Deploying
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a WebStack Application"</a> and write it into&nbsp;<code>MyAdapter.py</code>.</li>
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  <li>Now, with two files in your directory, <code>MyApplication.py</code>
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and <code>MyAdapter.py</code>, you may run&nbsp;<code>MyAdapter.py</code>
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as follows:</li>
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</ol>
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<pre>python MyAdapter.py</pre>
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<p>This should start the adapter program and print the following
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message:</p>
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<pre>Serving...</pre>
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<p>You should now be able to visit&nbsp;<code>http://localhost:8080</code>
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in your
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browser and see the message printed by your application:</p>
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<pre>Hello world.</pre>
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<h2>About Resources</h2>
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<ul>
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  <li><a href="resource-creation.html">How Resources are Created</a></li>
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  <li><a href="design.html">Application Design Considerations</a></li>
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</ul>
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</body>
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</html>