c# Http下载

1.首先是服务器上发布资源，如果资源时自定义格式，比如 .zidingyi结尾的后缀文件，需要在MIME类型上添加处理方式

需要注意的是.net里面要设置

System.Net.ServicePointManager.DefaultConnectionLimit = 50;

2.客户端采用WebRequest进行请求，WebRequest处理响应

 /// <summary>
    /// Http协议下载助手
    /// </summary>
    public class HttpDownLoadHelper
    {
        #region 变量,属性
        private HttpWebRequest request;
        private HttpWebResponse response;
        public string SavePath { get; set; }
        public string URL { get; set; }
        public string State { get; set; }
        private int iReConnectTimes = 0;//重连次数
        public long DownLoadedSize { get; set; }//已下载大小
        private bool IFAbortExec = true;//是否异常中断
        FileStream fs;
        Stream reader;
        #endregion
        #region 构造函数
        public HttpDownLoadHelper()
        {
        }
        public HttpDownLoadHelper(string vsServerFilePath, string vsSavePath)
        {
            //request = (HttpWebRequest)HttpWebRequest.Create(new Uri(vsServerFilePath));
            this.URL = vsServerFilePath;
            SavePath = vsSavePath;
        }
        #endregion
        #region 方法
        /// <summary>
        /// 读取已下载文件大小
        /// </summary>
        public void Init()
        {
            if (File.Exists(SavePath))//断点续传
            {
                fs = File.OpenWrite(SavePath);
                DownLoadedSize = fs.Length;
                fs.Close();
            }
        }
        public void DownLoadFile(string vsServerFilePath, string vsSavePath)
        {
            URL = vsServerFilePath;
            SavePath = vsSavePath;
            DownLoadFile();
        }
        public void DownLoadFile()
        {
            try
            {
                request = (HttpWebRequest)HttpWebRequest.Create(new Uri(URL));
                request.KeepAlive = true;
                request.Timeout = 1000 * 10;
                request.ReadWriteTimeout = 1000 * 20;//不知道为啥，流read的时候会超时
                long startPos = 0;
                if (File.Exists(SavePath))//断点续传
                {
                    fs = File.OpenWrite(SavePath);
                    if (fs.Length > 0)//对于已下载的索引文件，重新下载最后一个字节，否则AddRange会出错，因为文件大小获取是总的
                    {
                        fs.Seek(fs.Length - 1, SeekOrigin.Current);
                        startPos = fs.Length - 1;
                    }
                    else
                    {
                        fs.Seek(fs.Length, SeekOrigin.Current);
                        startPos = fs.Length;
                    }
                }
                else//全新下载
                {
                    string vsDir = Path.GetDirectoryName(SavePath);
                    if (!Directory.Exists(vsDir))
                    {
                        Directory.CreateDirectory(vsDir);
                    }
                    fs = new FileStream(SavePath, FileMode.Create);
                    startPos = 0;
                }
                DownLoadedSize = startPos;
                if (!string.IsNullOrEmpty(State) && State.ToUpper() == "PAUSED")
                {
                    fs.Close();
                    return;
                }
                if (startPos > 0)
                {
                    request.AddRange(startPos);
                }
                byte[] buffer = new byte[1024 * 32];
                response = (HttpWebResponse)request.GetResponse();
                reader = response.GetResponseStream();
                int iRead = reader.Read(buffer, 0, buffer.Length);
                DownLoadedSize += iRead;
                while (iRead > 0)
                {
                    fs.Write(buffer, 0, iRead);
                    iRead = reader.Read(buffer, 0, buffer.Length);
                    DownLoadedSize += iRead;
                }
                fs.Close();
                reader.Close();
                if (response != null)
                {
                    response.Close();
                }
                if (request != null)
                {
                    request.Abort();
                }
            }
            catch (Exception ex)
            {
                if (IFAbortExec)
                {
                    Logger.LogError(ex);
                }
                //断线重连
                ++iReConnectTimes;
                if (iReConnectTimes > 5 || !IFAbortExec)//清理资源
                {
                    fs.Close();
                    if (reader != null)
                    {
                        reader.Close();
                    }
                    if (response != null)
                    {
                        response.Close();
                    }
                    if (request != null)
                    {
                        request.Abort();
                    }
                }
                else if (IFAbortExec)//异常中断才可重连,先清理资源
                {
                    fs.Close();
                    if (reader != null)
                    {
                        reader.Close();
                    }
                    if (response != null)
                    {
                        response.Close();
                    }
                    if (request != null)
                    {
                        request.Abort();
                    }
                    DownLoadFile();
                }

            }
        }
        public void GetDownLoadedSize()
        {
            long startPos = 0;
            if (File.Exists(SavePath))//断点续传
            {
                fs = File.OpenWrite(SavePath);
                fs.Seek(fs.Length, SeekOrigin.Current);
                startPos = fs.Length;
            }
            else//全新下载
            {
                fs = new FileStream(SavePath, FileMode.Create);
                startPos = 0;
            }
            DownLoadedSize = startPos;
        }
        public void Abort()
        {
            try
            {
                IFAbortExec = false;//非异常中断
                if (request != null)
                {
                    request.Abort();
                }
                if (response != null)
                {
                    response.Close();
                }
                if (fs != null)
                {
                    fs.Close();
                }
                if (reader != null)
                {
                    reader.Close();
                }
            }
            catch (Exception ex)
            {
                Logger.LogError(ex);
            }
        }
        public void Cancel()
        {
            Abort();
            //删除文件
            try
            {
                if (File.Exists(SavePath))
                {
                    File.Delete(SavePath);
                }
            }
            catch (Exception ex)
            {
                Logger.LogError(ex);
            }
        }
        #endregion
    }