1 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 2 <html xmlns="http://www.w3.org/1999/xhtml"> 3 <head> 4 <meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type" /> 5 <title>Applications and Resources</title> 6 <meta name="generator" 7 content="amaya 8.1a, see http://www.w3.org/Amaya/" /> 8 <link href="styles.css" rel="stylesheet" type="text/css" /> 9 </head> 10 <body> 11 <h1>Applications and Resources</h1> 12 At its simplest a WebStack application is just a single Python 13 class that we call a "resource". This class can be defined inside a 14 normal Python module or package, so let us start by doing the following:<br /> 15 <ol> 16 <li>Create a new directory for 17 our application; choose any name since we just want an empty space in 18 which to put new files.</li> 19 <li>Create a file called <code>MyApplication.py</code> 20 - this is our module.</li> 21 </ol> 22 We are going to call our resource <code>MyResource</code> 23 and in principle it will have a structure that looks like this: 24 <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> 25 <p>It is in this kind of resource 26 class that we write the 27 actual application code or at least the beginnings of it. When a user 28 of the application sends us a request, 29 the <code>respond</code> method 30 will be called and the code 31 within it executed. The parts of the pseudo-code in 32 the above text which aren't valid Python 33 (ie. the bits in square brackets) will, when we have written them, use 34 the <code>trans</code> 35 object to find out what any given user of the application has sent us, 36 and to send information back 37 to the 38 user in response.</p> 39 <h2>Starting Simple</h2> 40 <p>The simplest way to turn this 41 into a working application is to 42 ignore the first two activities mentioned in the pseudo-code and just 43 to produce some kind of 44 response. Here is how we can make our application do something:</p> 45 <ol> 46 <li>Edit the module 47 file <code>MyApplication.py</code>.</li> 48 <li>Write into it the following 49 code which defines <code>MyResource</code>:</li> 50 </ol> 51 <pre>class MyResource:<br /> def respond(self, trans):<br /> out = trans.get_response_stream()<br /> print >>out, "Hello world."</pre> 52 <h2>Testing the Resource</h2> 53 <p>To test this resource we need to deploy it, and to do that we need 54 an 55 adapter. Here is a quick way of writing an adapter and testing this 56 code:</p> 57 <ol> 58 <li> Create a file called <code>MyAdapter.py</code> - you 59 can choose another name if you want - this will be where the adapter 60 code lives.</li> 61 <li>Copy the example adapter in <a href="deploying.html">"Deploying 62 a WebStack Application"</a> and write it into <code>MyAdapter.py</code>.</li> 63 <li>Now, with two files in your directory, <code>MyApplication.py</code> 64 and <code>MyAdapter.py</code>, you may run <code>MyAdapter.py</code> 65 as follows:</li> 66 </ol> 67 <pre>python MyAdapter.py</pre> 68 <p>This should start the adapter program and print the following 69 message:</p> 70 <pre>Serving...</pre> 71 <p>You should now be able to visit <code>http://localhost:8080</code> 72 in your 73 browser and see the message printed by your application:</p> 74 <pre>Hello world.</pre> 75 <h2>About Resources</h2> 76 <ul> 77 <li><a href="resource-creation.html">How Resources are Created</a></li> 78 <li><a href="design.html">Application Design Considerations</a></li> 79 </ul> 80 </body> 81 </html>
