Http方式下载文件

using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Net;using System.Text;using System.Threading.Tasks;namespace WebSiteTest.Common{ ???public 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 ???????????????//} ???????????????return false; ???????????} ???????????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; ???????????} ???????} ???}}