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;
    }