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Seeing the adapter pattern in action - PHP

You may have already encountered situations in coding PHP applications in which you would like to use inheritance, but could not for one reason or another. Fortunately, there is an alternative for these situations that can help you achieve the same result. In this first article in a two-part series, you'll learn about the adapter pattern.

  1. The Basics of Implementing Adapter Objects with PHP
  2. The basics of adapter objects
  3. Defining a concrete directory processor class
  4. Seeing the adapter pattern in action
By: Alejandro Gervasio
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December 06, 2006

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As discussed in the previous section, one of the easiest ways to extend the functionality of a given class without having to use inheritance is simply by defining an adapter class. The adapter class will modify one or more methods of the original one to conform a specific model.

This being said, and based upon all the prior sample classes, here is the complete process for creating the aforementioned adapter class. Take a look, please:

// define abstract 'DirectoryProcessorAdapter' class abstract class AbstractDirectoryProcessorAdapter{       private $dirProcessor;       abstract public function getDetailedDirInfo(); } // define concrete 'DirectoryProcessorAdapter' class class DirectoryProcessorAdapter extends AbstractDirectoryProcessorAdapter{             // define constructor             public function __construct(DirectoryProcessor $dirProcessor){                         $this->dirProcessor=$dirProcessor;             }             // implements concretely 'fetchDetailedDirContent()' method             public function getDetailedDirInfo(){                         return '<h1>Detailed information about selected
directory is as follows:</h1><h2>Contents of selected directory is as follows:</h2>'.$this->dirProcessor->
fetchDirContent().'<h2>Data about selected directory is as follows:</h2>'.$this->dirProcessor->getDirInfo();             } }

As you can see, the above defined “DirectoryProcessorAdapter” class is now capable of extending the functionality of the previous “DirectoryProcessor” by simply injecting this object into the corresponding constructor, and finally defining the completely new “fetchDetailedDirContent()” method.

Here, it’s clear to see that this method combines the capacity of “fetchDirContent()” and “getDirInfo()” in one single block and displays the respective information on the browser. See how an adapter class now fits into the whole picture?

Now that you hopefully grasped the logic that drives the “DirectoryProcessorAdapter” class that you learned before, I’d like to go one step forward and show you how to properly use this class. Therefore, examine the example listed below, which demonstrates a simple implementation of the adapter class:

try{ // instantiate 'DirectoryProcessor' object         $dirProc=new DirectoryProcessor('default_path/');         // instantiate 'DirectoryProcessorAdapter' object         $dirProcAdapter=new DirectoryProcessorAdapter($dirProc); // display detailed information on selected director
(implements the adapter pattern)         echo $dirProcAdapter->getDetailedDirInfo(); } catch(Exception $e){     echo $e->getMessage();     exit(); } /* displays the following: Detailed information about selected directory is as follows: Contents of selected directory is as follows: . .. file1.txt file2.txt Data about selected directory is as follows: Name of selected directory is . and its basename is the following:
default_path */

As you’ll realize, the previous example demonstrates how easy it is to use the adapter class that I defined a few lines above. After a new directory processor object and its respective adapter have been instantiated, the “getDetailedDirInfo()” method is called up at the end of the script, which neatly displays the directory information detailed above. 

After all, implementing the adapter pattern with PHP 5 isn’t difficult. As you saw in the previous example, a given class can be easily modified without using inheritance, in cases where this approach is not viable.

To wrap up

We’ve come to the end of this first article. Hopefully, after learning all the concepts and examples given here, you’ll have a clearer idea of how to create an adapter class with PHP.

But this educational journey hasn’t ended yet, since in the second (and last) tutorial you’ll learn how to create an adapter that works in tandem with the standard “DirectoryIterator” class, included with PHP 5, in addition to building adapters for MySQL. Therefore, meet you in the last part!

>>> More PHP Articles          >>> More By Alejandro Gervasio

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