转载多线程下载(HTTPWebRequest)
下面是一个完整的多线程下载源码，我在写代码的时候遇到点问题也放在下面，希望大家别犯相同的错误。
问题1、线程偷懒？
在程序中我设置N个线程去下载时，然而有的线程却偷懒去了，当时非常奇怪，花了很多时间在代码上。
这其实是因为服务器不支持多线程下载造成的，大部分专业的下载站都禁止多线程下载，既然是服务器的原因那就没法了，在这里我想提一下在IIS7中启用和禁止多线程的方法。
应用程序池 -》 右击属性“高级设置” -》 进程模型 -》 最大工作进程数(这里便是设置允许多少线程)
至于IIS6也在应用程序池里设置，应用程序池- 》右击属性 -》 性能 -》 最大工作进程数。好了废话不说了，看下面的源码：
使用：
JhxzThreading mt = new JhxzThreading(5, “下载地址”, "本地保存路径");
mt.FileName = "wenjian"; //保存的文件名
mt.Start();
JhxzThreading公开了一些属性方便调用，如IsComplete表示这个下载任务是否完成，还有DownloadSize这个是实时下载了多少字节,通过这两个我们可以很容易实现进度条。如果有进度控件par：
pbar.Maximum = (int)mt.FileSize;
while (!mt.IsComplete)
{
pbar.Value = mt.DownloadSize;
}
上面虽然实现进度条了，但是由于主线程一直在循环的工作，窗体可能会有假死现象，针对这个原因我们专门用一个线程来控制进度。于是有了下面的做法。
pbar.Maximum = (int)mt.FileSize;
Thread bar = new Thread(() => {
while (!mt.IsComplete)
{
Thread.Sleep(50);
this.SafeInvoke(() => { pbar.Value = mt.DownloadSize; });
}
MessageBox.Show("恭喜！文件已下载完成","提示",MessageBoxButtons.OK,MessageBoxIcon.Information);
});
bar.Start();
多线程下载类：
public class JhxzThreading
{
private int _threadNum; //线程数量
private long _fileSize; //文件大小
private string _extName; //文件扩展名
private string _fileUrl; //文件地址
private string _fileName; //文件名
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
private Thread[] _thread; //线程数组
private List<string> _tempFiles = new List<string>();
public string FileName
{
get
{
return _fileName;
}
set
{
_fileName = value;
}
}
public long FileSize
{
get
{
return _fileSize;
}
}
public int DownloadSize
{
get
{
return _downloadSize;
}
}
public bool IsComplete
{
get
{
return _isComplete;
}
set
{
_isComplete = value;
}
}
public int ThreadNum
{
get
{
return _threadNum;
}
set
{
_threadNum = value;
}
}
public string SavePath
{
get
{
return _savePath;
}
set
{
_savePath = value;
}
}
public JhxzThreading(int threahNum, string fileUrl,string savePath)
{
this._threadNum = threahNum;
this._thread = new Thread[threahNum];
this._fileUrl = fileUrl;
this._savePath = savePath;
}
public void Start()
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(_fileUrl);
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
_extName = response.ResponseUri.ToString().Substring(response.ResponseUri.ToString().LastIndexOf('.'));//获取真实扩展名
_fileSize = response.ContentLength;
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++)
{
List<int> range = new List<int>();
range.Add(i * singelNum);
if (remainder != 0 && (_threadNum - 1) == i) //剩余的交给最后一个线程
range.Add(i * singelNum + singelNum + remainder - 1);
else
range.Add(i * singelNum + singelNum - 1);
_thread[i] = new Thread(() => { Download(range[0], range[1]); });
_thread[i].Name = "jhxz_{0}".Formart(i + 1);
_thread[i].Start();
}
}
private void Download(int from, int to)
{
Stream httpFileStream = null, localFileStram = null;
try
{
string tmpFileBlock = @"{0}\{1}_{2}.dat".Formart(_savePath, _fileName, Thread.CurrentThread.Name);
_tempFiles.Add(tmpFileBlock);
HttpWebRequest httprequest = (HttpWebRequest)WebRequest.Create(_fileUrl);
httprequest.AddRange(from, to);
HttpWebResponse httpresponse = (HttpWebResponse)httprequest.GetResponse();
httpFileStream = httpresponse.GetResponseStream();
localFileStram = new FileStream(tmpFileBlock, FileMode.Create);
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)
{
Thread.Sleep(20);
_downloadSize += getByteSize;
localFileStram.Write(by, 0, getByteSize);
getByteSize = httpFileStream.Read(by, 0, (int)by.Length);
}
_threadCompleteNum++;
}
catch (Exception ex)
{
throw new Exception(ex.Message.ToString());
}
finally
{
if (httpFileStream != null) httpFileStream.Dispose();
if (localFileStram != null) localFileStram.Dispose();
}
if (_threadCompleteNum == _threadNum)
{
_isComplete = true;
Complete();
}
}
private void Complete()
{
Stream mergeFile = new FileStream(@"{0}\{1}{2}".Formart(_savePath, _fileName, _extName), FileMode.Create);
BinaryWriter AddWriter = new BinaryWriter(mergeFile);
foreach (string file in _tempFiles)
{
using (FileStream fs = new FileStream(file, FileMode.Open))
{
BinaryReader TempReader = new BinaryReader(fs);
AddWriter.Write(TempReader.ReadBytes((int)fs.Length));
TempReader.Close();
}
File.Delete(file);
}
AddWriter.Close();
}
}
