php&cakephp显示图片的有关问题

private function outputFile2Brower(){        $filename=   WWW_ROOT."../../".$this->request->url;        if (!file_exists($filename)) {            throw RuntimeException("File $filename not found");        }        //TODO:这里应该智能判断type字符串        /*这个做法不对，容易导致一些图片无法显示        header("Content-Type:image/jpg");        header("Content-Length: ".filesize($filename));        readfile($filename);*/        $image = file_get_contents($filename);        //$content=addslashes($image);        header('Content-type: image/jpg');        echo $image;    }