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Document ID: 1412
Branch: main
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Name: Overview (unchanged)
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Updated on: 1/12/08 8:43:01 PM
Updated by: Grzegorz Kossakowski
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<li>Request's path is passed untouched.</li>
</ul>
+++ <h2>Inheritance and polymorphism</h2>
+++
+++ <p>Servlet can act as component thus it can extend other one and override
it's
+++ resource (request) handling. Nothing wrong is here, it's really about
overriding
+++ resource handling not methods of class implementing servlet interface. If
it was
+++ normal inheritance and polymorhism of classes then there would be no room
for
+++ innovation, Java has it all since 1.0 version.<br/>
+++ Servlet Service Framework cares only about <strong>resources</strong>
+++ (identified by URLs) particular servlet can handle and not about
implementation
+++ of servlet class. Basically, it means that all widely known concepts of
Object
+++ Oriented Programming are applied to resources. In order to help you
understand
+++ how various notions map from OOP to Resource Oriented Architecture (ROA)
take a
+++ look at following table:</p>
+++
+++ <table>
+++ <tbody>
+++ <tr>
+++ <th>
+++ <p>Object Oriented Programming</p>
+++ </th>
+++ <th>
+++ <p>Resource Oriented Architecture</p>
+++ </th>
+++ <th>
+++ <p>Remarks</p>
+++ </th>
+++ </tr>
+++ <tr>
+++ <td>
+++ <p>calling <tt>getFooBar()</tt> method</p>
+++ </td>
+++ <td>
+++ <p>requesting <tt>/fooBar</tt> resource</p>
+++ </td>
+++ <td>
+++ <p>for making request HTTP GET method is used</p>
+++ </td>
+++ </tr>
+++ <tr>
+++ <td>
+++ <p>calling <tt>getFooBar(value1, value2)</tt> method</p>
+++ </td>
+++ <td>
+++ <p>requesting <tt>/fooBar?param1=value1&param2=value2</tt> resource</p>
+++ </td>
+++ <td>
+++ <p>if one of parameters contains binary data, then POST (or PUT but we
won't get
+++ into details too much here) request is being made</p>
+++ </td>
+++ </tr>
+++ <tr>
+++ <td><tt>classB</tt>
+++ <p>extends <tt>classA</tt></p>
+++ </td>
+++ <td><tt>servletB</tt>
+++ <p>connects to <tt>servletA</tt> using connection named <tt>super</tt></p>
+++ </td>
+++ <td>
+++ <p>Connection named "super" is reserved for inheritance implementation</p>
+++ </td>
+++ </tr>
+++ <tr>
+++ <td valign="top"><tt>classA</tt>
+++ <p>implements <tt>interfaceB</tt></p>
+++ </td>
+++ <td valign="top">
+++ <p>N/A</p>
+++ </td>
+++ <td valign="top">
+++ <p>Servlet Service Framework does no have any equivalent for strong typing
known
+++ from programming languages so it cannot check if equivalent of interface is
+++ being implemented.<br/>
+++ The interface concept known from OOP maps best to just an abstract contract.
+++ It's a servletA's contract to handle various resources but check if it
really
+++ does can be made at runtime only. It's similar situation to scripting
languages
+++ like Javascript.</p>
+++ </td>
+++ </tr>
+++ <tr>
+++ <td valign="top"><tt>classB</tt>
+++ <p>overrides method <tt>getFooBar()</tt> implemented in <tt>classA</tt></p>
+++ </td>
+++ <td valign="top"><tt>servletB</tt>
+++ <p>implements handling of <tt>/fooBar</tt> resource.</p>
+++ </td>
+++ <td valign="top"/>
+++ </tr>
+++ </tbody>
+++ </table>
+++
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