C# Http文件下载公共类(支持断点续传)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Net;

namespace XcDownLoadFile
{
public class DownLoadFile
{
///
/// 下载文件方法
///
/// 文件保存路径和文件名
/// 返回服务器文件名
///
public bool DeownloadFile(string strFileName, string file)
{
bool flag = false;
//打开上次下载的文件
long SPosition = 0;
//实例化流对象
FileStream FStream;
//判断要下载的文件夹是否存在
if (File.Exists(strFileName))
{
//打开要下载的文件
FStream = File.OpenWrite(strFileName);
//获取已经下载的长度
SPosition = FStream.Length;
FStream.Seek(SPosition, SeekOrigin.Current);
}
else
{
//文件不保存创建一个文件
FStream = new FileStream(strFileName, FileMode.Create);
SPosition = 0;
}
try
{
//打开网络连接
HttpWebRequest myRequest = (HttpWebRequest)HttpWebRequest.Create("http://www.newxing.com/download/" + file);
if (SPosition > 0)
myRequest.AddRange((int)SPosition);             //设置Range值
//向服务器请求,获得服务器的回应数据流
Stream myStream = myRequest.GetResponse().GetResponseStream();
//定义一个字节数据
byte[] btContent = new byte[512];
int intSize = 0;
intSize = myStream.Read(btContent, 0, 512);
while (intSize > 0)
{
FStream.Write(btContent, 0, intSize);
intSize = myStream.Read(btContent, 0, 512);
}
//关闭流
FStream.Close();
myStream.Close();
flag = true;        //返回true下载成功
}
catch (Exception)
{
FStream.Close();
flag = false;       //返回false下载失败
}
return flag;
}
}
}