C#限速下载网络文件的方法实例

C#限速下载网络文件的方法，具体如下：

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Net;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using Common.Utils;
using Utils;

namespace 爬虫
{
public partial class Form1 : Form
{
#region 变量
/// <summary>
/// 已完成字节数
/// </summary>
private long completedCount = 0;
/// <summary>
/// 是否完成
/// </summary>
private bool isCompleted = true;
/// <summary>
/// 数据块队列
/// </summary>
private ConcurrentQueue<MemoryStream> msQueue = new ConcurrentQueue<MemoryStream>();
/// <summary>
/// 下载开始位置
/// </summary>
private long range = 0;
/// <summary>
/// 文件大小
/// </summary>
private long total = 0;
/// <summary>
/// 一段时间内的完成节点数，计算网速用
/// </summary>
private long unitCount = 0;
/// <summary>
/// 上次计时时间，计算网速用
/// </summary>
private DateTime lastTime = DateTime.MinValue;
/// <summary>
/// 一段时间内的完成字节数，控制网速用
/// </summary>
private long unitCountForLimit = 0;
/// <summary>
/// 上次计时时间，控制网速用
/// </summary>
private DateTime lastTimeForLimit = DateTime.MinValue;
/// <summary>
/// 下载文件sleep时间，控制速度用
/// </summary>
private int sleepTime = 1;
#endregion

#region Form1
public Form1()
{
InitializeComponent();
}
#endregion

#region Form1_Load
private void Form1_Load(object sender, EventArgs e)
{
lblMsg.Text = string.Empty;
lblByteMsg.Text = string.Empty;
lblSpeed.Text = string.Empty;
}
#endregion

#region Form1_FormClosing
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{

}
#endregion

#region btnDownload_Click 下载
private void btnDownload_Click(object sender, EventArgs e)
{
isCompleted = false;
btnDownload.Enabled = false;
string url = txtUrl.Text.Trim();
string filePath = CreateFilePath(url);

#region 下载线程
Thread thread = new Thread(new ThreadStart(() =>
{
int tryTimes = 0;
while (!HttpDownloadFile(url, filePath))
{
Thread.Sleep(10000);

tryTimes++;
LogUtil.Log("请求服务器失败，重新请求" + tryTimes.ToString() + "次");
this.Invoke(new InvokeDelegate(() =>
{
lblMsg.Text = "请求服务器失败，重新请求" + tryTimes.ToString() + "次";
}));
HttpDownloadFile(url, filePath);
}
}));
thread.IsBackground = true;
thread.Start();
#endregion

#region 保存文件线程
thread = new Thread(new ThreadStart(() =>
{
while (!isCompleted)
{
MemoryStream ms;
if (msQueue.TryDequeue(out ms))
{
using (FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Write))
{
fs.Seek(completedCount, SeekOrigin.Begin);
fs.Write(ms.ToArray(), 0, (int)ms.Length);
fs.Close();
}
completedCount += ms.Length;
}

if (total != 0 && total == completedCount)
{
Thread.Sleep(100);
isCompleted = true;
}

Thread.Sleep(1);
}
}));
thread.IsBackground = true;
thread.Start();
#endregion

#region 计算网速/进度线程
thread = new Thread(new ThreadStart(() =>
{
while (!isCompleted)
{
Thread.Sleep(1000);

if (lastTime != DateTime.MinValue)
{
double sec = DateTime.Now.Subtract(lastTime).TotalSeconds;
double speed = unitCount / sec / 1024;

try
{
#region 显示速度
if (speed < 1024)
{
this.Invoke(new InvokeDelegate(() =>
{
lblSpeed.Text = string.Format("{0}KB/S", speed.ToString("0.00"));
}));
}
else
{
this.Invoke(new InvokeDelegate(() =>
{
lblSpeed.Text = string.Format("{0}MB/S", (speed / 1024).ToString("0.00"));
}));
}
#endregion

#region 显示进度
this.Invoke(new InvokeDelegate(() =>
{
string strTotal = (total / 1024 / 1024).ToString("0.00") + "MB";
if (total < 1024 * 1024)
{
strTotal = (total / 1024).ToString("0.00") + "KB";
}
string completed = (completedCount / 1024 / 1024).ToString("0.00") + "MB";
if (completedCount < 1024 * 1024)
{
completed = (completedCount / 1024).ToString("0.00") + "KB";
}
lblMsg.Text = string.Format("进度：{0}/{1}", completed, strTotal);
lblByteMsg.Text = string.Format("已下载：{0}\r\n总大小：{1}", completedCount, total);

if (completedCount == total)
{
MessageBox.Show("完成");
}
}));
#endregion
}
catch { }

lastTime = DateTime.Now;
unitCount = 0;
}
}
}));
thread.IsBackground = true;
thread.Start();
#endregion

#region 限制网速线程
thread = new Thread(new ThreadStart(() =>
{
while (!isCompleted)
{
Thread.Sleep(100);

if (lastTimeForLimit != DateTime.MinValue)
{
double sec = DateTime.Now.Subtract(lastTimeForLimit).TotalSeconds;
double speed = unitCountForLimit / sec / 1024;

try
{
#region 限速/解除限速
double limitSpeed = 0;
if (double.TryParse(txtSpeed.Text.Trim(), out limitSpeed))
{
if (speed > limitSpeed && sleepTime < 1000)
{
sleepTime += 1;
}
if (speed < limitSpeed - 10 && sleepTime >= 2)
{
sleepTime -= 1;
}
}
else
{
this.Invoke(new InvokeDelegate(() =>
{
txtSpeed.Text = "100";
}));
}
#endregion
}
catch { }

lastTimeForLimit = DateTime.Now;
unitCountForLimit = 0;
}
}
}));
thread.IsBackground = true;
thread.Start();
#endregion

}
#endregion

#region HttpDownloadFile 下载文件
/// <summary>
/// Http下载文件
/// </summary>
public bool HttpDownloadFile(string url, string filePath)
{
try
{
if (!File.Exists(filePath))
{
using (FileStream fs = new FileStream(filePath, FileMode.Create))
{
fs.Close();
}
}
else
{
FileInfo fileInfo = new FileInfo(filePath);
range = fileInfo.Length;
}

// 设置参数
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)";
request.Proxy = null;
//发送请求并获取相应回应数据
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
if (response.ContentLength == range)
{
this.Invoke(new InvokeDelegate(() =>
{
lblMsg.Text = "文件已下载";
}));
return true;
}

// 设置参数
request = WebRequest.Create(url) as HttpWebRequest;
request.UserAgent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)";
request.Proxy = null;
request.AddRange(range);
//发送请求并获取相应回应数据
response = request.GetResponse() as HttpWebResponse;
//直到request.GetResponse()程序才开始向目标网页发送Post请求
Stream responseStream = response.GetResponseStream();

total = range + response.ContentLength;
completedCount = range;

MemoryStream ms = new MemoryStream();
byte[] bArr = new byte[1024];
lastTime = DateTime.Now;
lastTimeForLimit = DateTime.Now;
int size = responseStream.Read(bArr, 0, (int)bArr.Length);
unitCount += size;
unitCountForLimit += size;
ms.Write(bArr, 0, size);
while (!isCompleted)
{
size = responseStream.Read(bArr, 0, (int)bArr.Length);
unitCount += size;
unitCountForLimit += size;
ms.Write(bArr, 0, size);
if (ms.Length > 102400)
{
msQueue.Enqueue(ms);
ms = new MemoryStream();
}
if (completedCount + ms.Length == total)
{
msQueue.Enqueue(ms);
ms = new MemoryStream();
}

Thread.Sleep(sleepTime);
}
responseStream.Close();
return true;
}
catch (Exception ex)
{
LogUtil.LogError(ex.Message + "\r\n" + ex.StackTrace);
return false;
}
}
#endregion

#region 根据URL生成文件保存路径
private string CreateFilePath(string url)
{
string path = Application.StartupPath + "\\download";
if (!Directory.Exists(path))
{
Directory.CreateDirectory(path);
}

string fileName = Path.GetFileName(url);
if (fileName.IndexOf("?") > 0)
{
return path + "\\" + fileName.Substring(0, fileName.IndexOf("?"));
}
else
{
return path + "\\" + fileName;
}
}
#endregion

} //end Form1类
}

测试截图：

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