知识点：
1分段下载：httprequest.AddRange(begin, end);
2合并文件时，每个文件都有结束符“\0”。如：当1个文件下载为2个文件时，按顺序合并文件需要将第一个文件的结束符去掉，防止文件合并后的新文件与原始文件不一致。
源码下载：
关键代码：
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.IO;using System.Threading;using System.Net;namespace DownTest{ /// /// 下载文件类 /// public class MultiDownload { #region 变量 private int _threadNum; //线程数量 private long _fileSize; //文件大小 private string _fileUrl; //文件地址 private string _fileName; //文件名 private string _saverootpath = ""; private string _savePath; //保存路径 private short _threadCompleteNum; //线程完成数量 private bool _isComplete; //是否完成 private volatile int _downloadSize; //当前下载大小(实时的) private Thread[] _thread; //线程数组 private List _tempFiles = new List (); private object locker = new object(); #endregion #region 事件 public delegate void ReadHandler(DownStatus status, long size, long currentsize, Exception e); public event ReadHandler Reading; #endregion #region 属性 /// /// 下载状态 /// public DownStatus DownStatus { get; set; } /// /// 保存路径 /// public string SavePath { get { return _savePath; } } #endregion #region 构造函数 /// /// 构造函数 /// /// /// /// public MultiDownload(int threahNum, string fileUrl, string saverootpath) { var savePath = saverootpath + "\\" + System.IO.Path.GetFileName(fileUrl); this._saverootpath = saverootpath; this._threadNum = threahNum; this._thread = new Thread[threahNum]; this._fileUrl = fileUrl; this._savePath = savePath; this.DownStatus = DownStatus.None; } #endregion #region 检查是否有效 /// /// 检查是否有效 /// /// /// /// 开始任务 /// public void Start() { try { var msg = ""; var isvalid = IsValid(out msg); if (isvalid == false) { throw new Exception(msg); } //初始化全局变量 _threadCompleteNum = 0; _tempFiles = new List (); this.DownStatus = DownStatus.Downing; var readthread = new Thread(new ParameterizedThreadStart(ReadingThread)); readthread.Start(); HttpWebRequest request = (HttpWebRequest)WebRequest.Create(_fileUrl); HttpWebResponse response = (HttpWebResponse)request.GetResponse(); _fileSize = response.ContentLength; Console.WriteLine("_fileSize =" + _fileSize); int singelNum = (int)(_fileSize / _threadNum); //平均分配 int remainder = (int)(_fileSize % _threadNum); //获取剩余的 request.Abort(); response.Close(); for (int i = 0; i < _threadNum; i++) { var begin = singelNum * i; var end = singelNum * (i + 1); //最后一个进程，需要将剩余的也下载 if ((i + 1) == _threadNum) { end += remainder - 1; } //下载指定位置的数据 int[] ran = new int[] { begin, end }; _thread[i] = new Thread(new ParameterizedThreadStart(Download)); _thread[i].Name = System.IO.Path.GetFileNameWithoutExtension(_fileUrl) + "_{0}".Replace("{0}", Convert.ToString(i + 1)); _thread[i].Start(ran); } } catch (Exception e) { this.DownStatus = DownStatus.Stop; } } /// /// 检查下载进度进程 /// /// private void ReadingThread(object obj) { try { while (true) { try { long currentsize = 0; foreach (var file in _tempFiles) { if (File.Exists(file)) { FileInfo fileInfo = new FileInfo(file); currentsize += fileInfo.Length; } } //读取事件 if (Reading != null) { Reading(this.DownStatus, _fileSize, currentsize, null); } //结束进度进程 if (this.DownStatus != DownStatus.Downing) { break; } Thread.Sleep(1000); } catch (Exception ex) { } } } catch (Exception ex) { } } /// /// 下载文件进程 /// /// private void Download(object obj) { try { Stream httpFileStream = null, localFileStram = null; try { int[] ran = obj as int[]; var begin = ran[0]; var end = ran[1]; string tmpFileBlock = GetTmpPath() + Thread.CurrentThread.Name + ".tmp"; lock (locker) { //添加临时文件列表 if (_tempFiles.Contains(tmpFileBlock) == false) { _tempFiles.Add(tmpFileBlock); } } var seek = 0; var isneeddown = true; Console.WriteLine("tmpFileBlock=" + tmpFileBlock + "begin=" + begin + ",end=" + end); //如果文件已存在，则获取已下载长度，继续下载 if (File.Exists(tmpFileBlock)) { FileInfo fileInfo = new FileInfo(tmpFileBlock); var existlength = (int)fileInfo.Length; var needsize = end - begin + 1; Console.WriteLine("existlength=" + existlength + ",needsize=" + needsize + ",end=" + end + ",begin=" + begin); if (existlength > needsize) { //文件长度超过需要下载的长度，表示文件不是该任务创建的，需要删除，重新下载 File.Delete(tmpFileBlock); seek = 0; isneeddown = true; } else if (existlength == needsize) { //文件下载已完成 isneeddown = false; } else { //文件尚未下载完成，指定下载位置 begin = (existlength - 1);//已下载的长度-1（位置从0开始） seek = existlength;//已下载的长度 isneeddown = true; } } Console.WriteLine("isneeddown=" + isneeddown + "begin=" + begin + ",end=" + end + ",seek=" + seek); //判断是否需要下载数据 if (isneeddown) { HttpWebRequest httprequest = (HttpWebRequest)WebRequest.Create(_fileUrl); Console.WriteLine("begin =" + begin + ",end=" + end); Console.WriteLine("seek=" + seek); httprequest.AddRange(begin, end); HttpWebResponse httpresponse = (HttpWebResponse)httprequest.GetResponse(); httpFileStream = httpresponse.GetResponseStream(); //如果不存在，则新建 localFileStram = new FileStream(tmpFileBlock, FileMode.OpenOrCreate); //指定写入位置 localFileStram.Seek(seek, SeekOrigin.Begin); byte[] by = new byte[5000]; int getByteSize = httpFileStream.Read(by, 0, (int)by.Length); //Read方法将返回读入by变量中的总字节数 while (getByteSize > 0) { if (this.DownStatus == DownStatus.Stop) { throw new Exception("任务已停止！"); } Thread.Sleep(20); lock (locker) _downloadSize += getByteSize; localFileStram.Write(by, 0, getByteSize); getByteSize = httpFileStream.Read(by, 0, (int)by.Length); } } lock (locker) _threadCompleteNum++; } catch (Exception ex) { throw new Exception(ex.Message.ToString()); } finally { if (httpFileStream != null) httpFileStream.Dispose(); if (localFileStram != null) localFileStram.Dispose(); } if (_threadCompleteNum == _threadNum) { Complete(); _isComplete = true; this.DownStatus = DownStatus.Complete; } } catch (Exception e) { this.DownStatus = DownStatus.Stop; } } /// /// 下载完成后合并文件块 /// private void Complete() { Stream mergeFile = new FileStream(@_savePath, FileMode.Create); BinaryWriter AddWriter = new BinaryWriter(mergeFile); //按序号排序 _tempFiles.Sort(); int i = 0; foreach (string file in _tempFiles) { i++; using (FileStream fs = new FileStream(file, FileMode.Open)) { BinaryReader TempReader = new BinaryReader(fs); //由于一个文件拆分成多个文件时，每个文件最后都会拼接上结尾符"\0"，导致总长度多出(n-1)个字符，需要需要针对前面(n-1)个文件去除最后的"\0"。 if (i == _tempFiles.Count) { AddWriter.Write(TempReader.ReadBytes((int)fs.Length)); } else { AddWriter.Write(TempReader.ReadBytes((int)fs.Length - 1)); } TempReader.Close(); } } AddWriter.Close(); //删除临时文件夹 foreach (string file in _tempFiles) { //File.Delete(file); } } #endregion #region 删除临时文件 /// /// 删除临时文件 /// public void DeleteTmpFile() { this.DownStatus = DownStatus.Deleted; foreach (string file in _tempFiles) { File.Delete(file); } } #endregion #region 暂停任务 /// /// 暂停 /// public void Stop() { this.DownStatus = DownStatus.Stop; } #endregion #region 私有方法 /// /// 获取临时文件夹 /// ///