context.Response.ContentType = "text/plain";
            string filePath = context.Request.Params["path"];//文件相对路径
            if (FileExists(context.Server.MapPath(filePath)))
            {
                // 允许共享
                System.IO.Stream input = new System.IO.FileStream(context.Server.MapPath(filePath), System.IO.FileMode.Open, System.IO.FileAccess.ReadWrite, System.IO.FileShare.Inheritable);
                context.Response.ContentType = "application/octet-stream";
                //文件名
                string fileName = System.IO.Path.GetFileName(filePath);
                //文件名编码
                string encodingFileName = context.Server.UrlEncode(fileName).Replace('+', ' ');
                context.Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", encodingFileName));
                // 输出到 this.Response.OutputStream 中
                System.IO.Stream output = context.Response.OutputStream;
                // 创建一个块缓冲
                byte[] buffer = new byte[10 * 1024];
                // 手工关闭输出的缓存
                context.Response.BufferOutput = false;
                TransmitFile(input, output, buffer);
                output.Close();
                input.Close();
                context.Response.End();
            }

using System;
using System.Collections;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;

namespace Asiastar.NR.Ajax
{
    /// <summary>
    /// $codebehindclassname$ 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    public class Handler1 : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "text/plain";

            string id = context.Request["id"].ToString();//获取资源的编号
            System.IO.Stream iStream = null;
            byte[] buffer = new Byte[10000];
            int length;
            long dataToRead;
            NRBLL.File bf = new Asiastar.NRBLL.File();
            Guid guid = new Guid(id);
            if (bf.FN_SerchPathByFileId(guid).Tables[0].Rows[0]["FilePath"] != null)//判断数据库路径是否存在         
            {
                string filepath = bf.FN_SerchPathByFileId(guid).Tables[0].Rows[0]["FilePath"].ToString();//获取资源完整路径                   D:\资源文件\600cc139-14cf-448e-9e50-daa972d35e01.jpg
                string Oidfilename = bf.FN_SerchPathByFileId(guid).Tables[0].Rows[0]["FileNam"].ToString();//旧文件名称
                //string filename = System.IO.Path.GetFileName(filepath);//获取文件名称+后缀名            600cc139-14cf-448e-9e50-daa972d35e01.JPG
                //int index = filepath.IndexOf(".");
                //string filetype = filepath.Substring(index).ToLower();//后缀名
                //string newfilename = Oidfilename;
                //string filepath1 = bf.FN_SerchPathByFileId(guid).Tables[0].Rows[0]["FilePath"].ToString().Substring(0,filepath.Length - 8);
                try
                {
                    string fileName = HttpUtility.UrlEncode(System.Text.Encoding.UTF8.GetBytes(Oidfilename));//解码(注意这里2层解码)
                    Oidfilename = Oidfilename.Replace("+", "%20");  //将“+”替换成“空格”
                    iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read);
                    dataToRead = iStream.Length;