介绍php设计模式中的工厂模式
问题
你如何能轻松方便地建立这么" 复杂 " 的对象即操作中不需要粘贴复制呢?
解决方法
建立一个工厂(一个函数或一个类方法)来制造新的对象。为了理解工厂的用处, 试想以下的不同之处……
代码:
复制代码 代码如下:
$connection =& new MySqlConnection($user, $password, $database);
……使你的代码可扩展和更简洁……
复制代码 代码如下:
$connection =& create_connection();
后者的代码片断集中在和数据库连接的create_connect()工厂上 ,就像刚才说的一样,使创造数据库连接的过程成为一个简单的操作—就像new操作一样。工厂模式的优点就在创建对象上。 它的任务就是把对象的创建过程都封装起来,然后返回一个所需要的新类。
想改变对象的结构和建立对象的方式吗? 你只需选择对象工厂,对代码的改变只需要一次就够了。( 工厂模式的功能是如此强大, 它处于是应用的底层, 所以在许多其余的复杂模式和应用中它会不停地出现。)
样本代码
工厂模式封装了对象的建立过程。 你可以在对象本身创建对象工厂或者是一个额外的工厂类——这要看你具体的应用。让我们看一个工厂对象的例子。
我们发现下面代码中,数据库连接的那部分屡次出现:
复制代码 代码如下:
// PHP4
class Product {
function getList() { $db =& new MysqlConnection(DB_USER, DB_PW, DB_NAME);
//...
}
function getByName($name) { $db =& new MysqlConnection(DB_USER, DB_PW, DB_NAME);
//...
}
//...
}
你可以轻松地改变连接数据库的参数,但你不能增加或改变这些参数地顺序,除非你把所有连接代码都改了。
你不能轻松的实例化一个新类去连接另一种数据库,比如说PostgresqlConnection。
这样很难单独测试和证实连接对象的状态。
使用工厂设计模式,代码将得到很大的改进:
复制代码 代码如下:
class Product {
function getList() {
$db =& $this->_getConnection();
//...
}
function &_getConnection() {
return new MysqlConnection(DB_USER, DB_PW, DB_NAME);
}
}

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