C# http下载（支持断点续传）

分享下项目里面自己封装的一个http下载类

功能如下：

1、支持断点续传

2、下载失败自动重试

3、超时等异常处理

using System;using System.Collections.Generic;using System.IO;using System.Net;public class HttpManager{    const int bytebuff = 1024;    const int ReadWriteTimeOut = 2 * 1000;//超时等待时间    const int TimeOutWait = 5 * 1000;//超时等待时间    const int MaxTryTime = 12;    static Dictionary<string,int> TryNumDic = new Dictionary<string,int>();　　
    /// <summary>
    /// 下载文件（同步）  支持断点续传
    /// </summary>
    /// <param name="url">文件url</param>
    /// <param name="savepath">本地保存路径</param>
    /// <param name="progress">下载进度（百分比）</param>
    /// <param name="size">下载文件大小</param>    public static void DowLoadFile(string url,string savepath,ref int progress,long size = 0)    {        //打开上次下载的文件        long lStartPos = 0;        FileStream fs;        if(File.Exists(savepath))        {            fs = File.OpenWrite(savepath);            lStartPos = fs.Length;            fs.Seek(lStartPos,SeekOrigin.Current);//移动文件流中的当前指针        }        else        {            string direName = Path.GetDirectoryName(savepath);            if(!Directory.Exists(direName))//如果不存在保存文件夹路径，新建文件夹            {                Directory.CreateDirectory(direName);            }            fs = new FileStream(savepath, FileMode.Create);            lStartPos = 0;        }        HttpWebRequest request = null;        try{            if(size == 0)            {                size = GetFileContentLength(url);            }            if(size != 0 && size == lStartPos)            {                //下载完成                fs.Close();                return;            }            request = (HttpWebRequest)WebRequest.Create(url);            request.ReadWriteTimeout = ReadWriteTimeOut;            request.Timeout = TimeOutWait;            if(lStartPos>0)                request.AddRange((int)lStartPos);//设置Range值，断点续传            //向服务器请求，获得服务器回应数据流            WebResponse respone = request.GetResponse();            long totalSize = respone.ContentLength + lStartPos;            long curSize  = lStartPos;            progress  = (int)(curSize / totalSize *100);            Stream ns = respone.GetResponseStream();            byte[] nbytes = new byte[bytebuff];            int nReadSize = 0;            while(nReadSize > 0)            {                fs.Write(nbytes, 0, nReadSize);                nReadSize = ns.Read(nbytes, 0 ,bytebuff);                curSize += nReadSize;                //下载进度计算                if (progress < (int)((double)curSize / totalSize * 100))                    progress = (int)((double)curSize / totalSize * 100);                fs.Flush();                ns.Close();                fs.Close();                if(curSize!=totalSize)//文件长度不等于下载长度，下载出错                {                    throw new Exception();                }                if(request != null)                {                    request.Abort();                }                TryNumDic.Remove(url);            }        }        catch         {            if(request!=null)            {                request.Abort();            }                        fs.Close();            if(TryNumDic.ContainsKey(url))            {                if(TryNumDic[url]>MaxTryTime)                {                    TryNumDic.Remove(url);                    throw new Exception();                }                else                {                    TryNumDic[url]++;                }            }            else            {                TryNumDic.Add(url,1);            }            DowLoadFile(url, savepath, ref progress, size);        }    }    /// <summary>    /// 获取下载文件长度    /// </summary>    /// <param name="url"></param>    /// <returns></returns>    public static long GetFileContentLength(string url)    {        HttpWebRequest request = null;        try        {            request = (HttpWebRequest)HttpWebRequest.Create(url);            request.Timeout = TimeOutWait;            request.ReadWriteTimeout = ReadWriteTimeOut;            //向服务器请求，获得服务器回应数据流            WebResponse respone = request.GetResponse();            request.Abort();            return respone.ContentLength;        }        catch(Exception e)        {            if(request != null)                request.Abort();            return 0;        }    }}