1.说明

1.适配器模式： 能够将截然不同的函数接口封装成统一的API

2.实际应用举例，PHP的数据库操作有mysql, mysqli, pdo3种。能够用适配器模式统一成一致。相似的场景还有cache适配器，就是将memcache，redis，file，apc等不同的缓存函数统一成一致的

3.以下的样例能够帮助你对付各种数据库链接功能，mysql mysqli, pdo随便选，操作都抽象为统一的接口client不须要改动一行数据库链接方式

2.创建一个接口

interface IDatabase{
          function connect($host, $user, $passwd, $dbname);    function query($sql);    function close();}

3.Mysql封装

class MySQL implements IDatabase{
          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)    {
              $res = mysql_query($sql, $this->conn);        return $res;    }    function close()    {
              mysql_close($this->conn);    }}

4.MySqli封装

class MySQLi implements IDatabase{
          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);    }}

5.PDO封装

class PDO implements IDatabase{
          protected $conn;    function connect($host, $user, $passwd, $dbname)    {
              $conn = new \PDO("mysql:host=$host;dbname=$dbname", $user, $passwd);        $this->conn = $conn;    }    function query($sql)    {
              return $this->conn->query($sql);    }    function close()    {
              unset($this->conn);    }}

6.实例调用，（统一接口调用）

$db = new PDO();$db->connect('127.0.0.1', 'root', 'root', 'test');$db->query('show databases');$db->close();$db = MySQLi ();$db->connect('127.0.0.1', 'root', 'root', 'test');$db->query('show databases');$db->close();$db = MySQl PDO();$db->connect('127.0.0.1', 'root', 'root', 'test');$db->query('show databases');$db->close();