大话设计模式-命令模式

引自原书：

1.较容易地设计一个命令队列

2.在需要的情况下，可以容易地将命令记入日志

3.允许接收请求的一方决定是否要否决请求

4.可以容易地实现对请求的撤销和重做

5.由于加进新的具体命令类不影响其他的类，因此增加新的具体命令类很容易

6.命令模式把请求一个操作对象与知道怎么执行一个操作对象分割开【DP】

敏捷开发原则告诉我们，不要为代码添加基于猜测的、实际不需要的功能。如果不清楚一个系统是否需要命令模式，一般就不要着急去实现它，事实上，在需要的时候通过重构实现这个模式并不困难，只有在真正需要如撤销/恢复操作等功能时，把原来的代买重构为命令模式才有意义。【R2P】

//抽象命令abstract class Command {protected $receiver;function __construct(Barbecuer $receiver) {$this->receiver = $receiver;}//执行命令abstract public function excuteCommand();}//具体命令类//烤羊肉串命令class BakeMuttonCommand extends Command {function __construct(Barbecuer $receiver) {parent::__construct($receiver);}public function excuteCommand() {$this->receiver->bakeMutton();}}//烤鸡翅命令class BakeChickenWingCommand extends Command {function __construct(Barbecuer $receiver) {parent::__construct($receiver);}public function excuteCommand() {$this->receiver->bakeChickenWing();}}//烤肉串者class Barbecuer {//烤羊肉public function bakeMutton() {echo '烤羊肉串！<br/>';}//烤鸡翅public function bakeChickenWing() {echo '烤鸡翅！<br/>';}}//服务员class Waiter {private $orders;//设置订单public function setOrder(Command $command) {if($command instanceof BakeChickenWingCommand) {echo '服务员：鸡翅没了，请点别的烧烤。<br/>';} else if($command instanceof BakeMuttonCommand) {$this->orders[] = $command;echo '增加订单：烤羊肉 时间：'.date('Y-m-d H:i:s').'<br/>';}}//取消订单public function cancelOrder(Command $command) {unset($this->orders[array_search($command, $this->orders)]);}//通知全部执行public function notify() {foreach($this->orders as $cmd) {$cmd->excuteCommand();}}}//开店前的准备$boy = new Barbecuer();$bakeMuttonCommand1 = new BakeMuttonCommand($boy);$bakeMuttonCommand2 = new BakeMuttonCommand($boy);$bakeChickenWingCommand1 = new BakeChickenWingCommand($boy);$girl = new Waiter();//开门营业 顾客点菜$girl->setOrder($bakeMuttonCommand1);$girl->setOrder($bakeMuttonCommand2);$girl->setOrder($bakeChickenWingCommand1);//点菜完毕，通知厨房$girl->Notify();

//Command类，用来声明执行操作的接口abstract class Command {protected $receiver;function __construct(Receiver $receiver) {$this->receiver = $receiver;}abstract public function execute();}class ConcreteCommand extends Command {function __construct(Receiver $receiver) {parent::__construct($receiver);}public function execute() {$this->receiver->action();}}//Invoker类，要求该命令执行这个请求。class Invoker {private $command;public function setCommand(Command $command) {$this->command = $command;}public function executeCommand() {$this->command->execute();}}//Receiver类，知道如何实施与执行一个与请求相关的操作，任何类都可能作为一个接收者class Receiver {public function action() {echo '执行请求！<br/>';}}$r = new Receiver();$c = new ConcreteCommand($r);$i = new Invoker();$i->setCommand($c);$i->executeCommand();