php中将数据存储在session中的时候，会根据配置进行序列化，session_decode函数可以将session中的数据解码并重新存入$_SESSION这个全局变量中。但是如果仅仅需要解码后的数据，不需要重新存储到session中，就需要自己单独写函数来进行解码操作，具体代码如下：

// 请求入口
public function actionIndex($s_id='') {
        $session_id = $s_id;
        // '37qlrtm2vupsv6vmmi9nlbmdp5';
        $data = Yii::app()->session->readSession($session_id);
        $session_data = self::unserialize($data);
        echo CJSON::encode($session_data);
}

private static function unserialize($session_data) {
        $method = ini_get("session.serialize_handler");
        switch ($method) {
            case "php":
                return self::unserialize_php($session_data);
                break;
            case "php_binary":
                return self::unserialize_phpbinary($session_data);
                break;
            default:
                throw new Exception("Unsupported session.serialize_handler: " . $method . ". Supported: php, php_binary");
        }
    }

    private static function unserialize_php($session_data) {
        $return_data = array();
        $offset = 0;
        while ($offset < strlen($session_data)) {
            if (!strstr(substr($session_data, $offset), "|")) {
                throw new Exception("invalid data, remaining: " . substr($session_data, $offset));
            }
            $pos = strpos($session_data, "|", $offset);
            $num = $pos - $offset;
            $varname = substr($session_data, $offset, $num);
            $offset += $num + 1;
            $data = unserialize(substr($session_data, $offset));
            $return_data[$varname] = $data;
            $offset += strlen(serialize($data));
        }
        return $return_data;
    }

    private static function unserialize_phpbinary($session_data) {
        $return_data = array();
        $offset = 0;
        while ($offset < strlen($session_data)) {
            $num = ord($session_data[$offset]);
            $offset += 1;
            $varname = substr($session_data, $offset, $num);
            $offset += $num;
            $data = unserialize(substr($session_data, $offset));
            $return_data[$varname] = $data;
            $offset += strlen(serialize($data));
        }
        return $return_data;
    }