1、模式定义
责任链模式将处理请求的对象连成一条链，沿着这条链传递该请求，直到有一个对象处理请求为止，这使得多个对象都有机会处理请求，从而避免请求的发送者和接受者之间的耦合关系。
责任链模式在现实中使用的很多，常见的就是 OA 系统中的工作流。
2、UML 类图
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3、示例代码
Request.php
<?phpnamespace DesignPatterns\Behavioral\ChainOfResponsibilities;/** * 经过责任链的Request类 * * 关于请求: 有时候，不需要一个请求对象，只需一个整型数据或者一个数组即可。 * 但是作为一个完整示例，这里我们生成了一个请求类。 * 在实际项目中，也推荐使用请求类，即是是一个标准类\stdClass， * 因为这样的话代码更具扩展性，因为责任链的处理器并不了解外部世界， * 如果某天你想要添加其它复杂处理时不使用请求类会很麻烦 */class Request{ // getter and setter but I don't want to generate too much noise in handlers}Handler.php
<?phpnamespace DesignPatterns\Behavioral\ChainOfResponsibilities;/** * 责任链的通用处理器类Handler（通常是一个接口或抽象类） * * Yes you could have a lighter CoR with a simpler handler but if you want your CoR * to be extendable and decoupled, it's a better idea to do things like that in real * situations. Usually, a CoR is meant to be changed everytime and evolves, that's * why we slice the workflow in little bits of code. */abstract class Handler{ /** * @var Handler */ private $successor = null; /** * 追加处理类到责任链 * * A prepend method could be done with the same spirit * * You could also send the successor in the constructor but in PHP that is a * bad idea because you have to remove the type-hint of the parameter because * the last handler has a null successor. * * And if you override the constructor, that Handler can no longer have a * successor. One solution is to provide a NullObject (see pattern). * It is more preferable to keep the constructor "free" to inject services * you need with the DiC of symfony2 for example. * * @param Handler $handler */ final public function append(Handler $handler) { if (is_null($this->successor)) { $this->successor = $handler; } else { $this->successor->append($handler); } } /** * 处理请求 * * This approach by using a template method pattern ensures you that * each subclass will not forget to call the successor. Besides, the returned * boolean value indicates you if the request have been processed or not. * * @param Request $req * * @return bool */ final public function handle(Request $req) { $req->forDebugOnly = get_called_class(); $processed = $this->processing($req); if (!$processed) { // the request has not been processed by this handler => see the next if (!is_null($this->successor)) { $processed = $this->successor->handle($req); } } return $processed; } /** * 每个处理器具体实现类都要实现这个方法对请求进行处理 * * @param Request $req * * @return bool true if the request has been processed */ abstract protected function processing(Request $req);}Responsible/SlowStorage.php
<?phpnamespace DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible;use DesignPatterns\Behavioral\ChainOfResponsibilities\Handler;use DesignPatterns\Behavioral\ChainOfResponsibilities\Request;/** * This is mostly the same code as FastStorage but in fact, it may greatly differs * * One important fact about CoR: each item in the chain MUST NOT assume its position * in the chain. A CoR is not responsible if the request is not handled UNLESS * you make an "ExceptionHandler" which throws exception if the request goes there. * * To be really extendable, each handler doesn't know if there is something after it. * */class SlowStorage extends Handler{ /** * @var array */ protected $data = array(); /** * @param array $data */ public function __construct($data = array()) { $this->data = $data; } protected function processing(Request $req) { if ('get' === $req->verb) { if (array_key_exists($req->key, $this->data)) { $req->response = $this->data[$req->key]; return true; } } return false; }}Responsible/FastStorage.php
<?phpnamespace DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible;use DesignPatterns\Behavioral\ChainOfResponsibilities\Handler;use DesignPatterns\Behavioral\ChainOfResponsibilities\Request;/** * Class FastStorage */class FastStorage extends Handler{ /** * @var array */ protected $data = array(); /** * @param array $data */ public function __construct($data = array()) { $this->data = $data; } protected function processing(Request $req) { if ('get' === $req->verb) { if (array_key_exists($req->key, $this->data)) { // the handler IS responsible and then processes the request $req->response = $this->data[$req->key]; // instead of returning true, I could return the value but it proves // to be a bad idea. What if the value IS "false" ? return true; } } return false; }}4、测试代码
Tests/ChainTest.php
<?phpnamespace DesignPatterns\Behavioral\ChainOfResponsibilities\Tests;use DesignPatterns\Behavioral\ChainOfResponsibilities\Request;use DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\FastStorage;use DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\SlowStorage;use DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible;/** * ChainTest tests the CoR */class ChainTest extends \PHPUnit_Framework_TestCase{ /** * @var FastStorage */ protected $chain; protected function setUp() { $this->chain = new FastStorage(array('bar' => 'baz')); $this->chain->append(new SlowStorage(array('bar' => 'baz', 'foo' => 'bar'))); } public function makeRequest() { $request = new Request(); $request->verb = 'get'; return array( array($request) ); } /** * @dataProvider makeRequest */ public function testFastStorage($request) { $request->key = 'bar'; $ret = $this->chain->handle($request); $this->assertTrue($ret); $this->assertObjectHasAttribute('response', $request); $this->assertEquals('baz', $request->response); // despite both handle owns the 'bar' key, the FastStorage is responding first $className = 'DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\FastStorage'; $this->assertEquals($className, $request->forDebugOnly); } /** * @dataProvider makeRequest */ public function testSlowStorage($request) { $request->key = 'foo'; $ret = $this->chain->handle($request); $this->assertTrue($ret); $this->assertObjectHasAttribute('response', $request); $this->assertEquals('bar', $request->response); // FastStorage has no 'foo' key, the SlowStorage is responding $className = 'DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\SlowStorage'; $this->assertEquals($className, $request->forDebugOnly); } /** * @dataProvider makeRequest */ public function testFailure($request) { $request->key = 'kurukuku'; $ret = $this->chain->handle($request); $this->assertFalse($ret); // the last responsible : $className = 'DesignPatterns\Behavioral\ChainOfResponsibilities\Responsible\SlowStorage'; $this->assertEquals($className, $request->forDebugOnly); }}5、总结
责任链模式的主要优点在于可以降低系统的耦合度，简化对象的相互连接，同时增强给对象指派职责的灵活性，增加新的请求处理类也很方便；其主要缺点在于不能保证请求一定被接收，且对于比较长的职责链，请求的处理可能涉及到多个处理对象，系统性能将受到一定影响，而且在进行代码调试时不太方便。
