php用单例模式实现一个数据库类

 1 <?php
 2 class Danli
 3 {
 4 
 5 //保存类实例的静态成员变量
 6     private static $_instance;
 7 
 8 //private标记的构造方法
 9     private function __construct()
10     {
11         echo ‘This is a Constructed method;‘;
12     }
13 
14 //创建__clone方法防止对象被复制克隆
15     public function __clone()
16     {
17         trigger_error(‘Clone is not allow!‘, E_USER_ERROR);
18     }
19 
20 //单例方法,用于访问实例的公共的静态方法
21     public static function getInstance()
22     {
23         if (!(self::$_instance instanceof self)) {
24             self::$_instance = new self;
25         }
26         return self::$_instance;
27     }
28 
29     public function test()
30     {
31         echo ‘调用方法成功‘;
32     }
33 
34 }
35 
36 /*用new实例化private标记构造函数的类会报错
37 $danli = new Danli();
38 
39 复制(克隆)对象将导致一个E_USER_ERROR
40 $danli_clone = clone $danli;
41 */
42 
43 
44 //正确方法,用双冒号::操作符访问静态方法获取实例
45 $danli = Danli::getInstance();
46 $danli->test();
47 ?>

 1 <?php
 2 class DBHelper
 3 {
 4     private $link;
 5     static private $_instance;
 6 
 7     // 连接数据库
 8     private function __construct($host, $username, $password)
 9     {
10         $this->link = mysql_connect($host, $username, $password);
11         $this->query("SET NAMES ‘utf8‘", $this->link);
12         //echo mysql_errno($this->link) . ": " . mysql_error($link). "n";
13         //var_dump($this->link);
14         return $this->link;
15     }
16     private function __clone()
17     {
18     }
19     public static function get_class_nmdb($host, $username, $password)
20     {
21         //$connector = new nmdb($host, $username, $password);
22         //return $connector;
23 
24         if (FALSE == (self::$_instance instanceof self)) {
25             self::$_instance = new self($host, $username, $password);
26         }
27         return self::$_instance;
28     }
29     // 连接数据表
30     public function select_db($database)
31     {
32         $this->result = mysql_select_db($database);
33         return $this->result;
34     }
35     // 执行SQL语句
36     public function query($query)
37     {
38         return $this->result = mysql_query($query, $this->link);
39     }
40     // 将结果集保存为数组
41     public function fetch_array($fetch_array)
42     {
43         return $this->result = mysql_fetch_array($fetch_array, MYSQL_ASSOC);
44     }
45     // 获得记录数目
46     public function num_rows($query)
47     {
48         return $this->result = mysql_num_rows($query);
49     }
50     // 关闭数据库连接
51     public function close()
52     {
53         return $this->result = mysql_close($this->link);
54     }
55 }
56 $connector = DBHelper::get_class_nmdb($host, $username, $password);
57 $connector -> select_db($database);
58 ?>

 1 <?php
 2 /*
 3 * mysql 单例
 4 */
 5 class mysql{
 6     private $host    =‘localhost‘; //数据库主机
 7     private $user     = ‘root‘; //数据库用户名
 8     private $pwd     = ‘‘; //数据库用户名密码
 9     private $database = ‘imoro_imoro‘; //数据库名
10     private $charset = ‘utf8‘; //数据库编码，GBK,UTF8,gb2312
11     private $link;             //数据库连接标识;
12     private $rows;             //查询获取的多行数组
13     static $_instance; //存储对象
14     /**
15      * 构造函数
16      * 私有
17      */
18     private function __construct($pconnect = false) {
19         if (!$pconnect) {
20             $this->link = @ mysql_connect($this->host, $this->user, $this->pwd) or $this->err();
21         } else {
22             $this->link = @ mysql_pconnect($this->host, $this->user, $this->pwd) or $this->err();
23         }
24         mysql_select_db($this->database) or $this->err();
25         $this->query("SET NAMES ‘{$this->charset}‘", $this->link);
26         return $this->link;
27     }
28     /**
29      * 防止被克隆
30      *
31      */
32     private function __clone(){}
33     public static function getInstance($pconnect = false){
34         if(FALSE == (self::$_instance instanceof self)){
35             self::$_instance = new self($pconnect);
36         }
37         return self::$_instance;
38     }
39     /**
40      * 查询
41      */
42     public function query($sql, $link = ‘‘) {
43         $this->result = mysql_query($sql, $this->link) or $this->err($sql);
44         return $this->result;
45     }
46     /**
47      * 单行记录
48      */
49     public function getRow($sql, $type = MYSQL_ASSOC) {
50         $result = $this->query($sql);
51         return @ mysql_fetch_array($result, $type);
52     }
53     /**
54      * 多行记录
55      */
56     public function getRows($sql, $type = MYSQL_ASSOC) {
57         $result = $this->query($sql);
58         while ($row = @ mysql_fetch_array($result, $type)) {
59             $this->rows[] = $row;
60         }
61         return $this->rows;
62     }
63     /**
64      * 错误信息输出
65      */
66     protected function err($sql = null) {
67         //这里输出错误信息
68         echo ‘error‘;
69         exit();
70     }
71 }
72 //用例
73 $db = mysql::getInstance();
74 $db2 = mysql::getInstance();
75 $data = $db->getRows(‘select * from blog‘);
76 //print_r($data);
77 //判断两个对象是否相等
78 if($db === $db2){
79     echo ‘true‘;
80 }
81 ?>