S3:代理模式 Proxy

为其他对象提供一种代理以控制对这个对象的访问.

使用场合:

1.远程代理:为一个对象在不同的地址空间提供局部代表,隐藏对象存在于不同地址空间的事实.
2.虚拟代理:根据需要创建开销很大的对象,通过它来存放实例化需要很长时间的真实对象.
3.安全代理:用来控制真实对象访问时的权限.
4.智能指引:当调用真实对象时,代理处理另外一些事.

UML:

示例代码:

interface AbstractSubject
{public function connect();
}class RealSubject implements AbstractSubject
{public function connect(){echo 'link to db';}
}class ProxySubject implements AbstractSubject
{protected $real;public function __construct(){if (is_null($this->real)) {$this->real = new RealSubject();}}public function connect(){$this->real->connect();}
}$proxy = new ProxySubject();
$proxy->connect();

示例代码:

abstract class MySQL
{protected $link;protected function __construct(){$this->connect();}public function getAll($table){echo get_called_class() . PHP_EOL;$res = $this->link->query("SELECT * FROM {$table}");$data = array();foreach ($res as $row) {$data[] = $row;}return $data;}public function close(){$this->link = null;}abstract public static function getInstance();
}class ReadMySQL extends MySQL
{protected static $instance;public static function getInstance(){if (is_null(self::$instance)) {self::$instance = new self(); }return self::$instance;}public function connect(){if (is_null($this->link)) {$this->link = new PDO('mysql:host=127.0.0.1;dbname=test', 'root', 'root');}}
}class WriteMySQL extends MySQL
{protected static $instance;public static function getInstance(){if (is_null(self::$instance)) {self::$instance = new self(); }return self::$instance;}public function connect(){if (is_null($this->link)) {$this->link = new PDO('mysql:host=192.168.2.10;dbname=test', 'root', 'root');}}
}class ProxyMysql
{private $reader;private $writer;public function __construct(){$this->reader = ReadMySQL::getInstance();$this->writer = WriteMySQL::getInstance();}public function getAll($table){if (rand(1,2) === 1) {return $this->reader->getAll($table);} else {return $this->writer->getAll($table);}}
}$test = new ProxyMysql();
var_dump($test->getAll('test'));
var_dump($test->getAll('test'));
var_dump($test->getAll('test'));
var_dump($test->getAll('test'));

我们用ProxyMysql代理了ReaderMysql和WriterMysql,简单的随机判断从两台服务器读取数据.

转载于:https://www.cnblogs.com/itfenqing/p/7787804.html

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