设计模式-单例模式

<?php

/**
 * 单例模式
 * 
 * 以前写单例构造器的时候总是为如何把需要的参数传给类而烦恼
 * 
 *  如果项目中的类文件都采用这种设计的话就ok了
 * 
 *  每次获取实例的时候都可以更新资源变量
 */
class Utils_Common {

    private static $_instances = array();

    /**
     * 单例包装
     * @param 类名 $klass
     * @param 资源变量 $resource
     * @return null object
     */
    public static function getInstance($klass, $resource = null) {
        if (isset(self::$_instances[$klass])) {
            if (null !== $resource) {
                self::$_instances[$klass]->setResource($resource);
            }
            return self::$_instances[$klass];
        } else {
            if (class_exists($klass)) {
                self::$_instances[$klass] = new $klass($resource);
                return self::$_instances[$klass];
            } else {
                return null;
            }
        }
    }

}

class Db {

    //参数等资源
    private $resource;

    public function __construct($resource) {
        $this->resource = $resource;
    }

    public function setResource($resource) {
        $this->resource = $resource;
    }

    public function getResource() {
        return $this->resource;
    }

    protected function getRsrcParams($key) {
        return isset($this->resource[$key]) ? $this->resource[$key] : array();
    }

    protected function setRsrcParams($key, $value) {
        $this->resource[$key] = $value;
    }

    public function go() {
        echo 'success:' . $this->getRsrcParams('host');
    }

}

header('Content-Type:text/plain;charset=utf-8');
Utils_Common::getInstance('Db', array('host' => 'localhost'))->go();