思路：後臺點選上傳，然後上傳到指定位置，然後取得這個字串寫到資料庫

 <!--後臺那邊上傳檔案的標籤程式碼-->
  <form id="upload-form" action="" method="post" enctype="multipart/form-data" >
     <input type="file" class="input-text" id="upload" name="upload" />
     <input type="submit" class="btn btn-info" value="Upload" />
 </form
 
>

// 上傳檔案到指定目錄，然後資料庫儲存路徑
    public function fileupload()
    {
        if (IS_POST) {
            $file_size = $_FILES['upload']['size'];
            if ($file_size > 20 * 1024 * 1024) {
                echo "檔案過大，不能上傳大於20M的檔案";
                exit();
            }
            $dir = PACH."/Upload/sclass/"
 
;//檔案目錄 自己定義
            $fileName = time().uniqid().'.'.pathinfo($_FILES["upload"]["name"])['extension'];
            file_exists($dir) || (mkdir($dir,0777,true) && chmod($dir,0777));
            move_uploaded_file($_FILES["upload"]["tmp_name"],$dir.$fileName);
            $id = $_GET['id'];
            $data
 
['file'] = '/Upload/sclass/'.$fileName;
            $this->_model->where('id=43')->save($data);
        }

        $this->display();
    }

// 找到檔案路徑然後利用header方式進這個連結就下載
    public function uploadpdf(){
        $result = M('Information')->where('id=43')->field('file')->find();
        $urlInfo = pathinfo($result['file']);
        // 這邊點不要忘了
        $filePath =  '.'.$result['file'];
        $file = fopen($filePath, "r"); // 開啟檔案 // 輸入檔案標籤
        if ($file) {
            Header("Content-type:application/pdf");
            Header("Accept-Ranges: bytes");
            Header("Accept-Length: " . filesize($filePath));
            Header("Content-Disposition: attachment; filename=".$urlInfo['basename']); // 輸出檔案內容
            echo fread($file, filesize($filePath));
            fclose($file);
        }
    }

// 該二維碼的直接輸出
public function qrcode()
    {
        $url="http://".$_SERVER['SERVER_NAME']."/contact/uploadpdf.html";

        $level=3;
        $size=4;
        Vendor('Phpqrcode.phpqrcode');
        $errorCorrectionLevel =intval($level) ;//容錯級別
        $matrixPointSize = intval($size);//生成圖片大小
        //生成二維碼圖片
        $object = new \QRcode();
        $result = $object->png($url, false, $errorCorrectionLevel, $matrixPointSize, 2);
        return $result;
    }

<!--html標籤直接呼叫這個方法就行了-->
<img src="/contact/qrcode.html" alt="">

輸出text檔案給使用者
$date=date("Ymd");
$filename = $date."-".$this->user_id.".txt";
$fp = fopen('./plugins/bijidown/'.$filename, 'w') or die("Unable to open file!");
fwrite($fp, $str);
$fp = fopen('./plugins/bijidown/'.$filename, 'r') or die("Unable to open file!");
Header ( "Content-type: application/octet-stream" );
Header ( "Accept-Ranges: bytes" );
Header ( "Accept-Length: " . filesize ( './plugins/bijidown/' . $filename ) );
Header ( "Content-Disposition: attachment; filename=" . $filename );
//輸出檔案內容
//讀取檔案內容並直接輸出到瀏覽器
echo fread ( $fp, filesize ( './plugins/bijidown/' . $filename ) );
fclose ( $fp );
exit ();