解读工厂模式Factory Pattern

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JAVAEEME 2011-04-14 15:01:04

文章标签 职场休闲解读工厂模式 Factory Pattern 文章分类 前端开发

工厂类就是一个专门用来创建其它对象的类，工厂类在多态性编程实践中是非常重要的。它允许动态替换类，修改配置，会使应用程序更加灵活。掌握工厂模式对Web开发是必不可少的。

工厂模式通常用来返回类似接口的不同的类，工厂的一种常见用法就是创建多态的提供者。

通常工厂模式有一个关键的构造，即一般被命名为factory的静态方法。这个静态方法可以接受任意数量的参数，并且必须返回一个对象。

Program List：基本的工厂类

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<?php 

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    class Fruit { 

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        // 对象从工厂类返回 

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    } 

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    Class FruitFactory { 

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        public static function factory() { 

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            // 返回对象的一个新实例 

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            return new Fruit(); 

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        } 

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    } 

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    // 调用工厂 

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    $instance = FruitFactory::factory(); 

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?>

Program List：利用工厂类生产对象

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<?php 

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class Example 

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{ 

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    // The parameterized factory method 

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    public static function factory($type) 

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    { 

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        if (include_once 'Drivers/' . $type . '.php') { 

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            $classname = 'Driver_' . $type; 

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            return new $classname; 

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        } else { 

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            throw new Exception('Driver not found'); 

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        } 

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    } 

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} 

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// Load a MySQL Driver 

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$mysql = Example::factory('MySQL'); 

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// Load an SQLite Driver 

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$sqlite = Example::factory('SQLite'); 

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?>

Program List：一个完整的工厂类

下面的程序定义了一个通用的工厂类，它生产能够保存你所有操作的空对象，你可以获得一个实例，这些操作都在那个实例中了。

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<?php 

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    /** 

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     * Generic Factory class 

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     * 

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     * This Magic Factory will remember all operations you perform on it, 

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     * and apply them to the object it instantiates. 

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     * 

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     */

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    class FruitFactory { 

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        private $history, $class, $constructor_args; 

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        /** 

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         * Create a factory of given class. Accepts extra arguments to be passed to 

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         * class constructor. 

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         */

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        function __construct( $class ) { 

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            $args = func_get_args(); 

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            $this->class = $class; 

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            $this->constructor_args = array_slice( $args, 1 ); 

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        } 

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        function __call( $method, $args ) { 

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            $this->history[] = array( 

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                'action'    => 'call', 

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                'method'    => $method, 

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                'args'      => $args

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            ); 

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        } 

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        function __set( $property, $value ) { 

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            $this->history[] = array( 

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                'action'    => 'set', 

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                'property'    => $property, 

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                'value'        => $value

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            ); 

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        } 

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        /** 

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         * Creates an instance and performs all operations that were done on this MagicFactory 

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         */

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        function instance() { 

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            # use Reflection to create a new instance, using the $args 

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            $reflection_object = new ReflectionClass( $this->class );  

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            $object = $reflection_object->newInstanceArgs( $this->constructor_args );  

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            # Alternative method that doesn't use ReflectionClass, but doesn't support variable 

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            # number of constructor parameters. 

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            //$object = new $this->class(); 

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            # Repeat all remembered operations, apply to new object. 

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            foreach( $this->history as $item ) { 

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                if( $item['action'] == 'call' ) { 

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                    call_user_func_array( array( $object, $item['method'] ), $item['args'] ); 

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                } 

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                if( $item['action'] == 'set' ) { 

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                    $object->{$item['property']} = $item['value']; 

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                } 

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            } 

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            # Done 

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            return $object; 

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        } 

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    } 

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    class Fruit { 

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        private $name, $color; 

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        public $price; 

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        function __construct( $name, $color ) { 

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            $this->name = $name; 

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            $this->color = $color; 

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        } 

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        function setName( $name ) { 

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            $this->name = $name; 

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        } 

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        function introduce() { 

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            print "Hello, this is an {$this->name} {$this->sirname}, its price is {$this->price} RMB."; 

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        } 

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    } 

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    # Setup a factory 

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    $fruit_factory = new FruitFactory('Fruit', 'Apple', 'Gonn'); 

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    $fruit_factory->setName('Apple'); 

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    $fruit_factory->price = 2; 

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    # Get an instance 

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    $apple = $fruit_factory->instance(); 

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    $apple->introduce(); 

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?>