[ASP.net] 取得網路上的圖片並儲存在Server和Response給用戶端下載

2011-11-23

/*要先using以下兩個命名空間*/
using System.IO;
using System.Net;

 //Page_Load事件
 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string srcImageUrl = "https://chart.googleapis.com/chart?chs=120x120&cht=qr&chl=http://www.google.com.tw&choe=UTF-8&chld=M|2";

            //儲存圖片在Server上
            this.saveThumbPic(srcImageUrl, 100, Server.MapPath("~/test.jpg"));

            //Response給用戶端下載
            FileStream fs = new FileStream(Server.MapPath("~/test.jpg"), FileMode.Open);
            byte[] file = new byte[fs.Length];
            fs.Read(file, 0, file.Length);
            fs.Close();

            Response.Clear();
            Response.AddHeader("content-disposition", "attachment; filename=test.jpg");//強制下載
            Response.ContentType = "image/jpg";
            Response.BinaryWrite(file);

        }
    }

    #region 取得網路上的圖片
    /// <summary>
    /// 取得網路上的圖片
    /// </summary>
    /// <param name="strUrl">圖片的Url路徑</param>
    /// <returns>回傳 System.Drawing.Image物件</returns>
    public System.Drawing.Image getImageFromURL(string strUrl)
    {
        System.Drawing.Image MyImage = null;

        try
        {
            //建立一個 Web Request
            WebRequest MyWebRequest = WebRequest.Create(strUrl);
            //由 Web Request 取得 Web Response
            WebResponse MyWebResponse = MyWebRequest.GetResponse();
            //由 Web Response 取得 Stream
            Stream MyStream = MyWebResponse.GetResponseStream();
            //由 Stream 取得 Image
            MyImage = System.Drawing.Image.FromStream(MyStream);

            //該關的關一關, 該放的放一放
            MyStream.Close();
            MyStream.Dispose();
            MyWebResponse.Close();
            MyWebResponse = null;
            MyWebRequest = null;

        }
        catch (Exception ex)
        {
            throw new Exception("getImageFromURL(string strUrl)發生例外，可能抓不到網路上的圖片" + strUrl);
        }

        //回傳 Image
        return MyImage;
    }

    #endregion 


    #region [ASP.net程式使用]圖片等比例縮圖後的寬和高像素
    /// <summary>
    /// [ASP.net程式使用]取得圖片等比例縮圖後的寬和高像素
    /// </summary>
    /// <param name="image">System.Drawing.Image 的物件</param>
    /// <param name="maxPx">寬或高超過多少像素就要縮圖</param>
    /// <returns>回傳int陣列，索引0為縮圖後的寬度、索引1為縮圖後的高度</returns>
    public int[] getThumbPic_WidthAndHeight(System.Drawing.Image image, int maxPx)
    {

        int fixWidth = 0;

        int fixHeight = 0;

        if (image.Width > maxPx || image.Height > maxPx)
        //如果圖片的寬大於最大值或高大於最大值就往下執行  
        {

            if (image.Width >= image.Height)
            //圖片的寬大於圖片的高  
            {

                fixHeight = Convert.ToInt32((Convert.ToDouble(maxPx) / Convert.ToDouble(image.Width)) * Convert.ToDouble(image.Height));
                //設定修改後的圖高  
                fixWidth = maxPx;
            }
            else
            {

                fixWidth = Convert.ToInt32((Convert.ToDouble(maxPx) / Convert.ToDouble(image.Height)) * Convert.ToDouble(image.Width));
                //設定修改後的圖寬  
                fixHeight = maxPx;

            }



        }
        else
        {//圖片沒有超過設定值，不執行縮圖  

            fixHeight = image.Height;

            fixWidth = image.Width;

        }

        int[] fixWidthAndfixHeight = { fixWidth, fixHeight };



        return fixWidthAndfixHeight;
    }

    #endregion

    #region 產生縮圖並儲存
    /// <summary>
    /// 產生縮圖並儲存
    /// </summary>
    /// <param name="srcImageUrl">來源圖片的Url</param>
    /// <param name="maxPix">超過多少像素就要等比例縮圖</param>
    /// <param name="saveThumbFilePath">縮圖的儲存檔案路徑</param>
    public void saveThumbPic(string srcImageUrl, int maxPix, string saveThumbFilePath)
    {
        //為了callBack而callBack的寫法
        System.Drawing.Image.GetThumbnailImageAbort callBack =
             new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);


        //取得原始圖片
        System.Drawing.Image image = this.getImageFromURL(srcImageUrl);
        // 計算維持比例的縮圖大小
        int[] thumbnailScale = this.getThumbPic_WidthAndHeight(image, maxPix);
        // 產生縮圖
        System.Drawing.Image smallImage =
        image.GetThumbnailImage(thumbnailScale[0], thumbnailScale[1], callBack, IntPtr.Zero);
        // 將縮圖存檔
        smallImage.Save(saveThumbFilePath);
        // 釋放
        image.Dispose();
    }
    private bool ThumbnailCallback()
    {
        return false;
    }
    #endregion
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