C#实现文件下载，支持断点续传

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.IO;
using System.Text;
using System.Net;
namespace simpleDemo
{

class Program
{
    /// <summary>
    /// 下载文件保留字
    /// </summary>
    public static string PERSIST_EXP = ".cdel";
    /// <summary>  
    public static void Main(string[] args)
    {

        string path = "D:\\aa.txt";

        string ec = getFileEncoding(path, "GB2312");
        print("coding: " + ec);

        // string content = fileReader(path, Encoding.GetEncoding(ec));
        // print(content);

        //fileWriter(path, "测试内容11", Encoding.GetEncoding(ec));

        string url = "http://www.XXX.com/20120920172200024.flv";
        string path1 = "D:\\aa1.flv";


        download(url, path1);
        //gapDownload(url, path1);
        //t(url);

    }
    public static void t(string url) {

        HttpWebRequest request = (System.Net.HttpWebRequest)HttpWebRequest.Create(url);


        //WebResponse response = httpClient.CreateGetHttpResponse(url, 3000, null, null);

        try {

            WebResponse response = request.GetResponse();

            WebHeaderCollection headers = response.Headers;

            print(response.ContentLength);

            request = (System.Net.HttpWebRequest)HttpWebRequest.Create(url);
            request.AddRange(11); //设置Range值
            WebResponse response1 = request.GetResponse();
            print(response1.ContentLength);


            foreach (string key in headers)
            {
                print(key + "----- " + headers.Get(key));
            }

            string disposition = headers.Get("Content-Disposition");

            print(disposition);
        }catch(Exception e){
            print(e.Message);
        }

        //string fileName = disposition.Substring(disposition.IndexOf("\""));

        //print(fileName);

    }
    public static void download(string url, string path) {
        if (File.Exists(path))
        {
            print("文件己存在！是否重新下载？");
            return;
        }
        else {
            path = path + PERSIST_EXP;

            simpleDownload(url,path);//开始下载
        }   
    }
    /// <summary>
    /// 下载网络资源(支持断点续传)
    /// </summary>
    /// <param name="url"></param>
    /// <param name="path"></param>
    public static void simpleDownload(string url, string path)
    {
        HttpWebRequest request = httpClient.getWebRequest(url, 0);

        WebResponse response = null;

        FileStream writer = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);
        long lStartPos = writer.Length; ;//当前文件大小
        long currentLength = 0;
        long totalLength = 0;//总大小 

        if (File.Exists(path))//断点续传
        {
            response = request.GetResponse();
            long sTotal = response.ContentLength;

            if (sTotal == lStartPos) {

                close(writer);
                File.Move(path, path.Replace(PERSIST_EXP, ""));
                print("下载完成!");
                return;

            }
            request = httpClient.getWebRequest(url, (int)lStartPos);//设置Range值

            writer.Seek(lStartPos, SeekOrigin.Begin);//指针跳转
            response = request.GetResponse();

            totalLength = response.ContentLength + lStartPos; //总长度
            currentLength = lStartPos; //当前长度
        }
        else
        {
            response = request.GetResponse();
            totalLength = response.ContentLength;
        }

        Stream reader = response.GetResponseStream();

        byte[] buff = new byte[1024];
        int c = 0; //实际读取的字节数

        while ((c = reader.Read(buff, 0, buff.Length)) > 0)
        {
            currentLength += c;
            writer.Write(buff, 0, c);
            progressBar(currentLength, totalLength);//进度条

            writer.Flush();
        }
        close(writer);
        if (currentLength == totalLength)
        {
            File.Move(path, path.Replace(PERSIST_EXP, ""));
            print("下载完成!");
        }


        if (reader != null)
        {
            reader.Close();
            reader.Dispose();
            response.Close();
        }
    }
    private static void close(FileStream writer)
    {
        if (writer != null)
        {
            writer.Close();
            writer.Dispose();
        }
    }
    /// <summary>
    /// 进度条
    /// </summary>
    /// <param name="currentLength">当前长度</param>
    /// <param name="totalLength">总长度</param>
    public static void progressBar(Object currentLength, Object totalLength)
    {
        double aaa = System.Convert.ToDouble(currentLength);
        double bbb = System.Convert.ToDouble(totalLength);
        print(currentLength + "/" + totalLength + "__" + (aaa / bbb).ToString("0.00 %"));
    }
    /// <summary>
    /// 系统输出
    /// </summary>
    /// <param name="obj"></param>
    public static void print(Object obj){
        Console.WriteLine(obj);
    }
    public static void printStr(string[] str)
    {
        foreach (string d in str)
        {
            print(d);
        }
    }
    /// <summary>
    /// 文件写
    /// </summary>
    /// <param name="path">文件路径</param>
    /// <param name="content">要写入的内容</param>
    public static void fileWriter(string path,string content,Encoding encoding)
    {
        if (File.Exists(path))
        {
            StreamWriter sw = new StreamWriter(path, true, encoding);

            sw.WriteLine(content);

            sw.Flush();
            sw.Close();
        }
    }
    /// <summary>
    /// 读文件，返回内容
    /// </summary>
    /// <param name="path">文件路径</param>
    /// <param name="enCoding">默认编码格式</param>
    /// <returns></returns>
    public static string fileReader(string path,Encoding enCoding) {
        StringBuilder sb = new StringBuilder();
        if(enCoding == null){
            enCoding = Encoding.Default;
        }
        //读取文件
        StreamReader sr = new StreamReader(path, enCoding);
            string s = "";
            while ((s = sr.ReadLine()) != null)
            {
                sb.AppendLine(s);
            }
            if(sr != null)
                sr.Close();

        return sb.ToString();
    }
    /// <summary>
    /// 获取文件编码格式
    /// </summary>
    /// <param name="path">文件路径</param>
    /// <param name="defaultEncoding">默认编码</param>
    /// <returns></returns>
    public static string getFileEncoding(string path, string defaultEncoding) {
        string ed = defaultEncoding;
        if (File.Exists(path)) {
            FileStream fs = new FileStream(path, FileMode.Open);
            ed = GetEncoding(fs, defaultEncoding);
            if (fs != null)
                fs.Close();   
        }
        return ed;
    }
    /// <summary>
    /// 取得一个文本文件流的编码方式。
    /// </summary>
    /// <param name="stream">文本文件流。</param>
    /// <param name="defaultEncoding">默认编码方式。当该方法无法从文件的头部取得有效的前导符时，将返回该编码方式。</param>
    /// <returns></returns>
    public static string GetEncoding(FileStream stream, string defaultEncoding)
    {
        string targetEncoding = defaultEncoding;
        if (stream != null && stream.Length >= 2)
        {
            //保存文件流的前4个字节
            byte byte1 = 0;
            byte byte2 = 0;
            byte byte3 = 0;
            byte byte4 = 0;
            //保存当前Seek位置
            long origPos = stream.Seek(0, SeekOrigin.Begin);
            stream.Seek(0, SeekOrigin.Begin);

            int nByte = stream.ReadByte();
            byte1 = Convert.ToByte(nByte);
            byte2 = Convert.ToByte(stream.ReadByte());
            if (stream.Length >= 3)
            {
                byte3 = Convert.ToByte(stream.ReadByte());
            }
            if (stream.Length >= 4)
            {
                byte4 = Convert.ToByte(stream.ReadByte());
            }
            //根据文件流的前4个字节判断Encoding
            //Unicode {0xFF, 0xFE};
            //BE-Unicode {0xFE, 0xFF};
            //UTF8 = {0xEF, 0xBB, 0xBF};
            if (byte1 == 0xFE && byte2 == 0xFF)//UnicodeBe
            {
                targetEncoding = Encoding.BigEndianUnicode.BodyName;
            }
            if (byte1 == 0xFF && byte2 == 0xFE && byte3 != 0xFF)//Unicode
            {
                targetEncoding = Encoding.Unicode.BodyName;
            }
            if (byte1 == 0xEF && byte2 == 0xBB && byte3 == 0xBF)//UTF8
            {
                targetEncoding = Encoding.UTF8.BodyName;
            }
            //恢复Seek位置 
            stream.Seek(origPos, SeekOrigin.Begin);
        }
        return targetEncoding;
    }

}
 
}
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
using System.IO;
namespace simpleDemo
{
    /// <summary>
    /// 公用 Http 请求类
    /// </summary>
    class httpClient
    {
        /// <summary>
        /// 获取基础WebRequest
        /// </summary>
        /// <param name="url">请求地址</param>
        /// <param name="lStartPos">请求的开始位置</param>
        /// <returns></returns>
        public static HttpWebRequest getWebRequest(string url, int lStartPos)
        {
            HttpWebRequest request = null;
            try
            {
                request = (System.Net.HttpWebRequest)HttpWebRequest.Create(url);
                request.AddRange(lStartPos); //设置Range值
            }
            catch (Exception ex)
            {
                Program.print(ex.Message);
            }

        return request;
    }
}
 
}</pre>