ASP.NET 2.0 文件下载（支持大文件、防盗链）

1.文件下载
HTTP 文件下载主要有两种方式：
URL方式直接下载，优点是：占用服务器资源少，速度快；缺点是：不能准确计量下载次数，无法防止盗链，保存在数据库中的文件无法下载，常见格式的文件如.html 直接在浏览器中打开，不能直接下载。
二进制数据流输出方式，优点是：准确计量下载次数、能防盗链、所有文件格式都能直接下载而不是打开、保存在数据库中等非文件数据能以文件方式下载等；缺点是占用服务器资源多。
大文件下载原理是把文件切成小段数据流下载，微软msdn给出了大文件下载的示例，但存在中文文件名乱码问题，稍加改动即可。代码为：

protected void ResponseFile(string path) { 
    System.IO.Stream iStream = null; 
    byte[] buffer = new Byte[10000]; 
    int length; 
    long dataToRead; 
    string filename = System.IO.Path.GetFileName(path); 
  
    try { 
        iStream = new System.IO.FileStream(path, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read); 
        dataToRead = iStream.Length; 
        Response.ContentType = "application/octet-stream"; 
        Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8)); 
        while (dataToRead > 0) { 
            if (Response.IsClientConnected) { 
                length = iStream.Read(buffer, 0, 10000); 
                Response.OutputStream.Write(buffer, 0, length); 
                Response.Flush(); 
                buffer = new Byte[10000]; 
                dataToRead = dataToRead - length; 
                } 
            else { 
                dataToRead = -1; 
                } 
            } 
        } 
    catch (Exception ex) { 
        Response.Write("文件下载时出现错误!"); 
        } 
        finally { 
            if (iStream != null) { 
                iStream.Close(); 
                } 
            } 
        }

protected void ResponseFile(string path) { 	System.IO.Stream iStream = null; 	byte[] buffer = new Byte[10000]; 	int length; 	long dataToRead; 	string filename = System.IO.Path.GetFileName(path); 	try { 		iStream = new System.IO.FileStream(path, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read); 		dataToRead = iStream.Length; 		Response.ContentType = "application/octet-stream"; 		Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(filename, System.Text.Encoding.UTF8)); 		while (dataToRead > 0) { 			if (Response.IsClientConnected) { 				length = iStream.Read(buffer, 0, 10000); 				Response.OutputStream.Write(buffer, 0, length); 				Response.Flush(); 				buffer = new Byte[10000]; 				dataToRead = dataToRead - length; 				} 			else { 				dataToRead = -1; 				} 			} 		} 	catch (Exception ex) { 		Response.Write("文件下载时出现错误!"); 		} 		finally { 			if (iStream != null) { 				iStream.Close(); 				} 			} 		}

2.防止盗链

protected void Page_Load(object sender, EventArgs e) { 
    /*-------------大文件下载，防盗链------------------*/
    if (Request.QueryString["FileName"] == null) { InvalidRedirect(); } 
    string fileName = Request.QueryString["FileName"]; 
    if (fileName == string.Empty) { InvalidRedirect(); } 
    //判断配置文件是否直接下载 
    string downDirect = ConfigurationManager.AppSettings["Down"].ToLower(); 
    if (downDirect == "true") { UpdateHits(fileName); 
    //更新下载次数 Response.Redirect("Upload/" + fileName);  return; } 
    string path = Server.MapPath(Request.ApplicationPath + "/Upload/" + fileName); 
    string referrer = string.Empty; 
    if (Request.UrlReferrer != null) { referrer = Request.UrlReferrer.ToString().ToLower(); } 
    string d = ConfigurationManager.AppSettings["Valid"].ToLower(); 
    string[] domainName = ConfigurationManager.AppSettings["Refers"].ToLower().Split(new char[] { ',' }); 
    // 如果设置为防止盗链，判断访问来源是否合法 
    if (d == "false") { 
        foreach (string s in domainName) { 
            if (referrer.IndexOf(s.ToLower()) > 0) { UpdateHits(fileName); 
            //更新下载次数 
            ResponseFile(path); 
            return; 
            } 
            } 
        InvalidRedirect(); 
        } 
        else { 
            ResponseFile(path); 
            } 
        } 
    protected void UpdateHits(string fileName) { 
        //更新文件下载次数的代码 
        } 
    protected void InvalidRedirect() { 
        string defaultPage = ConfigurationManager.AppSettings["DefaultRedirect"]; 
        Response.Redirect(defaultPage, true); 
        }

protected void Page_Load(object sender, EventArgs e) { 	/*-------------大文件下载，防盗链------------------*/ 	if (Request.QueryString["FileName"] == null) { InvalidRedirect(); } 	string fileName = Request.QueryString["FileName"]; 	if (fileName == string.Empty) { InvalidRedirect(); } 	//判断配置文件是否直接下载 	string downDirect = ConfigurationManager.AppSettings["Down"].ToLower(); 	if (downDirect == "true") { UpdateHits(fileName); 	//更新下载次数 Response.Redirect("Upload/" + fileName); return; } 	string path = Server.MapPath(Request.ApplicationPath + "/Upload/" + fileName); 	string referrer = string.Empty; 	if (Request.UrlReferrer != null) { referrer = Request.UrlReferrer.ToString().ToLower(); } 	string d = ConfigurationManager.AppSettings["Valid"].ToLower(); 	string[] domainName = ConfigurationManager.AppSettings["Refers"].ToLower().Split(new char[] { ',' }); 	// 如果设置为防止盗链，判断访问来源是否合法 	if (d == "false") { 		foreach (string s in domainName) { 			if (referrer.IndexOf(s.ToLower()) > 0) { UpdateHits(fileName); 			//更新下载次数 			ResponseFile(path); 			return; 			} 			} 		InvalidRedirect(); 		} 		else { 			ResponseFile(path); 			} 		} 	protected void UpdateHits(string fileName) { 		//更新文件下载次数的代码 		} 	protected void InvalidRedirect() { 		string defaultPage = ConfigurationManager.AppSettings["DefaultRedirect"]; 		Response.Redirect(defaultPage, true); 		}

3.配置文件
配置文件中配置下载方式、盗链功能是否开启及盗链默认转向的页面地址：

<appSettings> 
    <add key="Down" value="false"/> 
    <!--是否直接下载--> 
    <add key="Valid" value="false"/> 
    <!--是否允许盗链--> 
    <add key="Refers" value="localhost,google.cn"/> 
    <!--多个允许的访问来源用半角的","分割--> 
    <add key="DefaultRedirect" value="Error.htm"/> 
    <!--默认转向的页面--> 
</appSettings>