purpose
Dynamically add functionality to instances of the class
example
Zend Framework: Decorator of Zend_Form_Element instances
Web Service layer: JSON and XML decorators for REST services (Of course, only one of them can be used here)
UML graphics
Code
- RenderableInterface.php
<?php
namespace DesignPatterns\Structural\Decorator;
/**
* 创建渲染接口。
* 这里的装饰方法 renderData() 返回的是字符串格式数据。
*/
interface RenderableInterface
{
public function renderData(): string;
}- Webservice.php
<?php
namespace DesignPatterns\Structural\Decorator;
/**
* 创建 Webservice 服务类实现 RenderableInterface。
* 该类将在后面为装饰者实现数据的输入。
*/
class Webservice implements RenderableInterface
{
/**
* @var string
*/
private $data;
/**
* 传入字符串格式数据。
*/
public function __construct(string $data)
{
$this->data = $data;
}
/**
* 实现 RenderableInterface 渲染接口中的 renderData() 方法。
* 返回传入的数据。
*/
public function renderData(): string
{
return $this->data;
}
}- RendererDecorator.php
<?php
namespace DesignPatterns\Structural\Decorator;
/**
* 装饰者必须实现渲染接口类 RenderableInterface 契约，这是该设计
* 模式的关键点。否则，这将不是一个装饰者而只是一个自欺欺人的包
* 装。
*
* 创建抽象类 RendererDecorator （渲染器装饰者）实现渲染接口。
*/
abstract class RendererDecorator implements RenderableInterface
{
/**
* @var RenderableInterface
* 定义渲染接口变量。
*/
protected $wrapped;
/**
* @param RenderableInterface $renderer
* 传入渲染接口类对象 $renderer。
*/
public function __construct(RenderableInterface $renderer)
{
$this->wrapped = $renderer;
}
}- XmlRenderer.php
<?php
namespace DesignPatterns\Structural\Decorator;
/**
* 创建 Xml 修饰者并继承抽象类 RendererDecorator 。
*/
class XmlRenderer extends RendererDecorator
{
/**
* 对传入的渲染接口对象进行处理，生成 DOM 数据文件。
*/
public function renderData(): string
{
$doc = new \DOMDocument();
$data = $this->wrapped->renderData();
$doc->appendChild($doc->createElement('content', $data));
return $doc->saveXML();
}
}- JsonRenderer.php
<?php
namespace DesignPatterns\Structural\Decorator;
/**
* 创建 Json 修饰者并继承抽象类 RendererDecorator 。
*/
class JsonRenderer extends RendererDecorator
{
/**
* 对传入的渲染接口对象进行处理，生成 JSON 数据。
*/
public function renderData(): string
{
return json_encode($this->wrapped->renderData());
}
}test
- Tests/DecoratorTest.php
<?php
namespace DesignPatterns\Structural\Decorator\Tests;
use DesignPatterns\Structural\Decorator;
use PHPUnit\Framework\TestCase;
/**
* 创建自动化测试单元 DecoratorTest 。
*/
class DecoratorTest extends TestCase
{
/**
* @var Decorator\Webservice
*/
private $service;
/**
* 传入字符串 'foobar' 。
*/
protected function setUp()
{
$this->service = new Decorator\Webservice('foobar');
}
/**
* 测试 JSON 装饰者。
* 这里的 assertEquals 是为了判断返回的结果是否符合预期。
*/
public function testJsonDecorator()
{
$service = new Decorator\JsonRenderer($this->service);
$this->assertEquals('"foobar"', $service->renderData());
}
/**
* 测试 Xml 装饰者。
*/
public function testXmlDecorator()
{
$service = new Decorator\XmlRenderer($this->service);
$this->assertXmlStringEqualsXmlString('<?xml version="1.0"?><content>foobar</content>', $service->renderData());
}
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