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.