using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net;namespace ConsoleTest
{class HttpDldFile{/// <summary>/// Http方式下载文件/// </summary>/// <param name="url">http地址</param>/// <param name="localfile">本地文件</param>/// <returns></returns>public bool Download(string url,string localfile){bool flag = false;long startPosition = 0; // 上次下载的文件起始位置FileStream writeStream; // 写入本地文件流对象long remoteFileLength = GetHttpLength(url);// 取得远程文件长度System.Console.WriteLine("remoteFileLength=" + remoteFileLength);if (remoteFileLength==745){System.Console.WriteLine("远程文件不存在.");return false;}// 判断要下载的文件夹是否存在if (File.Exists(localfile)){writeStream = File.OpenWrite(localfile);             // 存在则打开要下载的文件startPosition = writeStream.Length;                  // 获取已经下载的长度if (startPosition >= remoteFileLength){System.Console.WriteLine("本地文件长度" + startPosition + "已经大于等于远程文件长度" + remoteFileLength);writeStream.Close();return false;}else{writeStream.Seek(startPosition, SeekOrigin.Current); // 本地文件写入位置定位
                }}else{writeStream = new FileStream(localfile, FileMode.Create);// 文件不保存创建一个文件startPosition = 0;}            try{HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create(url);// 打开网络连接if (startPosition > 0){myRequest.AddRange((int)startPosition);// 设置Range值,与上面的writeStream.Seek用意相同,是为了定义远程文件读取位置
                }Stream readStream = myRequest.GetResponse().GetResponseStream();// 向服务器请求,获得服务器的回应数据流byte[] btArray = new byte[512];// 定义一个字节数据,用来向readStream读取内容和向writeStream写入内容int contentSize = readStream.Read(btArray, 0, btArray.Length);// 向远程文件读第一次long currPostion=startPosition;while (contentSize > 0)// 如果读取长度大于零则继续读
                {currPostion+=contentSize;int percent = (int)(currPostion*100/ remoteFileLength);System.Console.WriteLine("percent=" + percent + "%");writeStream.Write(btArray, 0, contentSize);// 写入本地文件contentSize = readStream.Read(btArray, 0, btArray.Length);// 继续向远程文件读取
                }//关闭流
                writeStream.Close();readStream.Close();flag = true;        //返回true下载成功
            }catch (Exception){writeStream.Close();flag = false;       //返回false下载失败
            }return flag;}// 从文件头得到远程文件的长度private static long GetHttpLength(string url){long length=0;try{HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);// 打开网络连接HttpWebResponse rsp = (HttpWebResponse)req.GetResponse();if (rsp.StatusCode == HttpStatusCode.OK){length = rsp.ContentLength;// 从文件头得到远程文件的长度
                }rsp.Close();return length;}catch(Exception e){return length;}}}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace ConsoleTest
{class Program{static void Main(string[] args){HttpDldFile df = new HttpDldFile();df.Download("http://files.cnblogs.com/files/xiandedanteng/Convertor20170624.zip","C:\\test\\Convertor20170624.zip");}}
}