PHP的单例模式代码

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单例模式，一个类只允许实例化一个对象，节约内存。

上代码：

<?php

header("Content-Type:text/html;charset=utf8");

//定义最终的单利的数据库操作类
final class Db{
	private static $obj = null;

	//私有的数据库配置信息
	private $dbHost;
	private $dbName;
	private $dbUser;
	private $dbPass;
	private $charset;

	//私有的构造方法
	private function __construct($conf){
		$this -> dbHost = $conf[&#39;dbHost&#39;];
		$this -> dbUser = $conf[&#39;dbUser&#39;];
		$this -> dbName = $conf[&#39;dbName&#39;];
		$this -> dbPass = $conf[&#39;dbPass&#39;];
		$this -> charset = $conf[&#39;charset&#39;];
		$this->connectDb();
		$this->selectDb();
		$this->setCharset();
	}

	//私有的克隆方法
	private function __clone(){}
	public static function getInstance($conf){
		if(!self::$obj instanceof self){
			self::$obj = new self($conf);
		}
		return self::$obj;
	}

	//私有的连接数据库方法
	private function connectDb(){
		if(!@mysql_connect($this->dbHost,$this->dbUser,$this->dbPass)){
			die(&#39;PHP连接mysql出错&#39;);
		}
	}

	//私有的选择数据库方法
	private function selectDb(){
		if(!mysql_select_db($this->dbName)){
			die(&#39;连接数据库出错&#39;);
		}
	}

	//私有的选择字符集方法
	private function setCharset(){
		mysql_set_charset($this->charset);
	}

	//将sql语句分为两类，返回结果集和返回布尔值
	//返回布尔值
	public function exec($sql){
		//将sql语句转化为小写
		$sql = strtolower($sql);
		//判断是否为select语句
		if(substr($sql,0,6) == &#39;select&#39;){
			die(&#39;不能执行select语句&#39;);
		}
		return mysql_query($sql);
	}

	//私有的执行select语句（结果集不能直接展示给前端，得经过处理返给对象）
	private function query($sql){
		//将sql语句转化为小写
		$sql = strtolower($sql);
		//判断是否为select语句
		if(substr($sql,0,6) != &#39;select&#39;){
			die(&#39;只能执行select语句&#39;);
		}
		return mysql_query($sql);
		
	}
	
	//将查询到的结果集返回给前端(返回一条)
	public function fetchOne($sql,$type=3){
		$res = $this ->query($sql);
		$types = array(
				1 => MYSQL_NUM,
				2 => MYSQL_ASSOC,
				3 => MYSQL_BOTH,
			);
		//返回一条记录
		return mysql_fetch_array($res,$types[$type]);
	}

	//将查询到的结果集返回给前端(返回多条)
	public function fetchAll($sql,$type=2){
		$res = $this ->query($sql);
		$types = array(
				1 => MYSQL_NUM,
				2 => MYSQL_ASSOC,
				3 => MYSQL_BOTH,
			);
		while($row = mysql_fetch_array($res,$types[$type])){
			$arr[] = $row;
		}
		return $arr;
	}
	//公共的获取记录数的方法
	public function getCount($sql){
		$res= $this ->query($sql);
		return mysql_num_rows($res);
	}
}

测试代码：

<?php

header("Content-Type:text/html;charset=utf8");

//类的自动加载

spl_autoload_register(function ($className){
	$arr = array(
		"./libs/{$className}.class.php",
	);
	foreach($arr as $path){
		if(file_exists($path)){
			require_once($path);
		}
	}
});
$arr = array(
	&#39;dbHost&#39; => &#39;localhost&#39;,
	&#39;dbUser&#39; => &#39;root&#39;,
	&#39;dbPass&#39; => &#39;root&#39;,
	&#39;dbName&#39; => &#39;test&#39;,
	&#39;charset&#39; => &#39;utf8&#39;,
);
$db = Db::getInstance($arr);
$sql = "select * from account where id = 100;";
var_dump($db->fetchOne($sql,2));

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