实现多线程下载文件

引用命名空间：

using System.Net;//网络功能 
using System.IO;//流支持
using System.Threading;//线程支持

 定义线程下载主体：

 public class threadbody
    {        
        Program p;
        int i;
        public threadbody( Program t_p,int t_i)
        {
            p = t_p;
            i = t_i;
        }

        public void Download()
        {
            try
            {
                string filename = p.filenamew[i];
                FileStream fsteam=new FileStream(filename, System.IO.FileMode.Create);
                HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(p.StrUrl);
                request.AddRange(p.filestartw[i], p.filestartw[i] + p.filesizew[i]);//设置Range值
                //向服务器请求，获得服务器回应数据流
                System.IO.Stream ns = request.GetResponse().GetResponseStream();
                byte[] nbytes = new byte[1024];
                int nReadSize = 0;
                nReadSize = ns.Read(nbytes, 0, 1024);
                while (nReadSize > 0)
                {
                    fsteam.Write(nbytes, 0, nReadSize);
                    nReadSize = ns.Read(nbytes, 0, 1024);
                }

                fsteam.Close();
                ns.Close();
               Console.WriteLine("线程{0}下载完成", i);
               p.threadw[i] = true;//表明此线程结束。
            }

            catch (Exception ex)
            {

                //p.fs.Close();

                Console.WriteLine("下载过程中出现错误:" + ex.ToString());

            }            

        }
    }

下载类：

   public class Program
    {
        public int[] filestartw = new int[5];//每个线程接收文件的起始位置
        public int[] filesizew = new int[5];//每个线程接收文件的大小
        public bool hb;//文件合并标志
        public string[] filenamew = new string[5];//每个线程接收文件的文件名
        public bool[] threadw = new bool[5]; //每个线程结束标志
        public int[] threadcount = new int[5] { 0, 0, 0, 0, 0 };
        public string StrUrl = "http://www.baidu.com/index.html";   //根据实际情况设置
        //string StrFileName = ;
        // public FileStream fs = new FileStream("D:\aa.rmvb", System.IO.FileMode.Create);

        /// <summary>
        /// 下面代码用于合并5个子文件。
        /// </summary>
        public void hbfile()
        {
            while (true)//等待
            {
                hb = true;
                for (int i = 0; i < 5; i++)
                {
                    if (threadw[i] == false)//有未结束线程，等待
                    {
                        hb = false;
                        Thread.Sleep(100);
                        break;
                    }
                }
                if (hb == true)//所有线程均已结束，停止等待，
                {
                    break;
                }
            }
            //FileStream fs;//开始合并
            if (hb == true)
            {
                Console.WriteLine("开始合并");
                FileStream fs = new FileStream("D:\temp.html", System.IO.FileMode.Create);
                FileStream fstemp;
                int readfile;
                byte[] bytes = new byte[512];
                for (int k = 0; k < 5; k++)
                {
                    fstemp = new FileStream(filenamew[k], System.IO.FileMode.Open);
                    while (true)
                    {
                        readfile = fstemp.Read(bytes, 0, 512);
                        if (readfile > 0)
                        {
                            fs.Write(bytes, 0, readfile);
                        }
                        else
                        {
                            break;
                        }
                    }
                    fstemp.Close();
                }
                fs.Close();
            }

        }
        /// <summary>
        /// 接受数据
        /// </summary>
        public void receive()
        {
            HttpWebRequest request;
            int filesize = 0;
            //int filesizeend = 0;//最后一个线程的大小
            //第一次请求是为了得到文件的大小
            try
            {
                while (true)
                {
                    request = (HttpWebRequest)HttpWebRequest.Create(StrUrl);
                    filesize = Convert.ToInt32(request.GetResponse().ContentLength); //取得目标文件的长度
                    if (filesize > 0)
                        break;
                }
                filesize = filesize / 20;
                //filesize = filesize / 5;//每个线程1%文件
                //filesizeend = filesize + (int)filesize % 5;//最后一个块的大小
                request.Abort();//结束这次请求
            }
            catch (Exception er)
            {
                Console.WriteLine(er.Message);
            }

            for (int i = 0; i < 5; i++)
            {
                threadw[i] = false;//每个线程状态的初始值为假
                filenamew[i] = i.ToString() + ".dat";//每个线程接收文件的临时文件名
                if (i < 4)
                {
                    filestartw[i] = filesize * i;//每个线程接收文件的起始点
                    filesizew[i] = filesize - 1;//每个线程接收文件的长度
                }
                else
                {
                    filestartw[i] = filesize * i;
                    filesizew[i] = filesize - 1;
                }
            }

            //定义线程数组，启动接收线程
            Thread[] threadk = new Thread[5];
            threadbody[] body = new threadbody[5];
            for (int j = 0; j < 5; j++)
            {
                body[j] = new threadbody(this, j);
                threadk[j] = new Thread(new ThreadStart(body[j].Download));
                threadk[j].Start();
            }
        }

        /// <summary>
        /// 主方法，开启5个线程下载。
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {
            Program p1 = new Program();
            p1.receive();
            p1.hbfile();

        }
    }