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