purpose
Create a chain of objects to process calls in a specified order. If one of the objects cannot process the command, it will delegate the call to the next object to process it, and so on.
example
Spam filter.
In the log framework, each chain element independently decides how to process log messages.
Cache: For example, the first object is an instance of the Memcached interface. If "lost" it will delegate the database interface to handle the call.
Yii framework: CFilterChain is a controller behavior filter chain. At the execution point, the filters on the chain are passed one by one, and only when all the filters are verified, this behavior will be called at the end.
UML graphics
Code
- Handler.php
<?php
namespace DesignPatterns\Behavioral\ChainOfResponsibilities;
use Psr\Http\Message\RequestInterface;
use Psr\Http\Message\ResponseInterface;
/**
* 创建处理器抽象类 Handler 。
*/
abstract class Handler
{
/**
* @var Handler|null
* 定义继承处理器
*/
private $successor = null;
/**
* 输入集成处理器对象。
*/
public function __construct(Handler $handler = null)
{
$this->successor = $handler;
}
/**
* 通过使用模板方法模式这种方法可以确保每个子类不会忽略调用继
* 承。
*
* @param RequestInterface $request
* 定义处理请求方法。
*
* @return string|null
*/
final public function handle(RequestInterface $request)
{
$processed = $this->processing($request);
if ($processed === null) {
// 请求尚未被目前的处理器处理 => 传递到下一个处理器。
if ($this->successor !== null) {
$processed = $this->successor->handle($request);
}
}
return $processed;
}
/**
* 声明处理方法。
*/
abstract protected function processing(RequestInterface $request);
}- Responsible/FastStorage.php
<?php
namespace DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible;
use DesignPatterns\Behavioral\ChainOfResponsibilities\Handler;
use Psr\Http\Message\RequestInterface;
/**
* 创建 http 缓存处理类。
*/
class HttpInMemoryCacheHandler extends Handler
{
/**
* @var array
*/
private $data;
/**
* @param array $data
* 传入数据数组参数。
* @param Handler|null $successor
* 传入处理器类对象 $successor 。
*/
public function __construct(array $data, Handler $successor = null)
{
parent::__construct($successor);
$this->data = $data;
}
/**
* @param RequestInterface $request
* 传入请求类对象参数 $request 。
* @return string|null
*
* 返回缓存中对应路径存储的数据。
*/
protected function processing(RequestInterface $request)
{
$key = sprintf(
'%s?%s',
$request->getUri()->getPath(),
$request->getUri()->getQuery()
);
if ($request->getMethod() == 'GET' && isset($this->data[$key])) {
return $this->data[$key];
}
return null;
}
}- Responsible/SlowStorage.php
<?php
namespace DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible;
use DesignPatterns\Behavioral\ChainOfResponsibilities\Handler;
use Psr\Http\Message\RequestInterface;
/**
* 创建数据库处理器。
*/
class SlowDatabaseHandler extends Handler
{
/**
* @param RequestInterface $request
* 传入请求类对象 $request 。
*
* @return string|null
* 定义处理方法，下面应该是个数据库查询动作，但是简单化模拟，直接返回一个 'Hello World' 字符串作查询结果。
*/
protected function processing(RequestInterface $request)
{
// 这是一个模拟输出， 在生产代码中你应该调用一个缓慢的 （相对于内存来说） 数据库查询结果。
return 'Hello World!';
}
}test
- Tests/ChainTest.php
<?php
namespace DesignPatterns\Behavioral\ChainOfResponsibilities\Tests;
use DesignPatterns\Behavioral\ChainOfResponsibilities\Handler;
use DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\HttpInMemoryCacheHandler;
use DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\SlowDatabaseHandler;
use PHPUnit\Framework\TestCase;
/**
* 创建一个自动化测试单元 ChainTest 。
*/
class ChainTest extends TestCase
{
/**
* @var Handler
*/
private $chain;
/**
* 模拟设置缓存处理器的缓存数据。
*/
protected function setUp()
{
$this->chain = new HttpInMemoryCacheHandler(
['/foo/bar?index=1' => 'Hello In Memory!'],
new SlowDatabaseHandler()
);
}
/**
* 模拟从缓存中拉取数据。
*/
public function testCanRequestKeyInFastStorage()
{
$uri = $this->createMock('Psr\Http\Message\UriInterface');
$uri->method('getPath')->willReturn('/foo/bar');
$uri->method('getQuery')->willReturn('index=1');
$request = $this->createMock('Psr\Http\Message\RequestInterface');
$request->method('getMethod')
->willReturn('GET');
$request->method('getUri')->willReturn($uri);
$this->assertEquals('Hello In Memory!', $this->chain->handle($request));
}
/**
* 模拟从数据库中拉取数据。
*/
public function testCanRequestKeyInSlowStorage()
{
$uri = $this->createMock('Psr\Http\Message\UriInterface');
$uri->method('getPath')->willReturn('/foo/baz');
$uri->method('getQuery')->willReturn('');
$request = $this->createMock('Psr\Http\Message\RequestInterface');
$request->method('getMethod')
->willReturn('GET');
$request->method('getUri')->willReturn($uri);
$this->assertEquals('Hello World!', $this->chain->handle($request));
}
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