适配器模式

可以将截然不同的函数接口封装成统一的API

下面用数据库的连接来演示适配器模式，一下是每个php文件主要代码，省略部分代码，如：命名空间，类的自动加载等代码

定义一个database接口，mysql、mysqli、pdo三种连接数据库的方式统一继承这个接口

Database.php

<?php
/**
* 接口
*/
interface Database
{
    function connect($host, $user, $passwd, $dbname);
    function query($sql);
    function close();
}

MYSQL.php

<?php
/**
* mysql方式连接数据库
*/
class MYSQL implements Database
{
    protected $conn;
    function connect($host, $user, $passwd, $dbname)
    {
        $conn = mysql_connect($host, $user, $passwd);
        mysql_select_db($dbname, $conn);
        $this->conn = $conn;
    }
    function query($sql)
    {
        return mysql_query($sql, $this->conn);
    }
    function close()
    {
        mysql_close($this->conn);
    }
}

MYSQLi.php

<?php
/**
* mysqli方式连接数据库
*/
class MYSQLi implements Database
{
    protected $conn;
    function connect($host, $user, $passwd, $dbname)
    {
        $conn = mysqli_connect($host, $user, $passwd, $dbname);
        $this->conn = $conn;
    }
    function query($sql)
    {
        return mysqli_query($this->conn, $sql);
    }
    function close()
    {
        mysqli_close($this->conn);
    }
}

PDO.php

<?php
/**
* PDO方式连接数据库
*/
class PDO implements Database
{
    protected $conn;
    function connect($host, $user, $passwd, $dbname)
    {
        $conn = new \PDO('mysql:host=$host;dbname=$dbname', $user, $password);
        $this->conn = $conn;
    }
    function query($sql)
    {
        return $this->conn->query($sql);
    }
    function close()
    {
        unset($this->conn);
    }
}

index.php

<?php
/**
* 调用以上三个数据库连接类型中一种
*/
$db = new ...\Database\数据库.php;
$db->connect('localhost', 'root', 'root', 'test');
$db->query('show databases');
$db->close();