C# 文件下载断点续传

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

namespace CHD.Framework
{
public class HttpDownLoadExtender
{
public static string PERSIST_EXP = ".cdel";

public static void download(string url, string path)
{
if (File.Exists(path))
{
print("文件己存在！是否重新下载？");
return;
}
else
{
path = path + PERSIST_EXP;

simpleDownload(url, path);//开始下载
}
}
/// <summary>
/// 下载网络资源(支持断点续传)
/// </summary>
/// <param name="url"></param>
/// <param name="path"></param>
public static void simpleDownload(string url, string path)
{
HttpWebRequest request = httpClient.getWebRequest(url, 0);
request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.110 Safari/537.36";
WebResponse response = null;

FileStream writer = new FileStream(path, FileMode.OpenOrCreate, FileAccess.Write);
long lStartPos = writer.Length; ;//当前文件大小
long currentLength = 0;
long totalLength = 0;//总大小

if (File.Exists(path))//断点续传
{
response = request.GetResponse();
long sTotal = response.ContentLength;

if (sTotal == lStartPos) {

close(writer);
File.Move(path, path.Replace(PERSIST_EXP, ""));
print("下载完成!");
return;

}
request = httpClient.getWebRequest(url, (int)lStartPos);//设置Range值

writer.Seek(lStartPos, SeekOrigin.Begin);//指针跳转
response = request.GetResponse();

totalLength = response.ContentLength + lStartPos; //总长度
currentLength = lStartPos; //当前长度
}
else
{
response = request.GetResponse();
totalLength = response.ContentLength;
}

Stream reader = response.GetResponseStream();

byte[] buff = new byte[1024];
int c = 0; //实际读取的字节数

while ((c = reader.Read(buff, 0, buff.Length)) > 0)
{
currentLength += c;
writer.Write(buff, 0, c);
progressBar(currentLength, totalLength);//进度条

writer.Flush();
}
close(writer);
if (currentLength == totalLength)
{
File.Move(path, path.Replace(PERSIST_EXP, ""));
print("下载完成!");
}

if (reader != null)
{
reader.Close();
reader.Dispose();
response.Close();
}
}
private static void close(FileStream writer)
{
if (writer != null)
{
writer.Close();
writer.Dispose();
}
}
/// <summary>
/// 进度条
/// </summary>
/// <param name="currentLength">当前长度</param>
/// <param name="totalLength">总长度</param>
public static void progressBar(Object currentLength, Object totalLength)
{
double aaa = System.Convert.ToDouble(currentLength);
double bbb = System.Convert.ToDouble(totalLength);
print(currentLength + "/" + totalLength + "__" + (aaa / bbb).ToString("0.00 %"));
}
/// <summary>
/// 系统输出
/// </summary>
/// <param name="obj"></param>
public static void print(Object obj){
Console.WriteLine(obj);
}
public static void printStr(string[] str)
{
foreach (string d in str)
{
print(d);
}
}
/// <summary>
/// 文件写
/// </summary>
/// <param name="path">文件路径</param>
/// <param name="content">要写入的内容</param>
public static void fileWriter(string path,string content,Encoding encoding)
{
if (File.Exists(path))
{
StreamWriter sw = new StreamWriter(path, true, encoding);

sw.WriteLine(content);

sw.Flush();
sw.Close();
}
}
/// <summary>
/// 读文件，返回内容
/// </summary>
/// <param name="path">文件路径</param>
/// <param name="enCoding">默认编码格式</param>
/// <returns></returns>
public static string fileReader(string path,Encoding enCoding) {
StringBuilder sb = new StringBuilder();
if(enCoding == null){
enCoding = Encoding.Default;
}
//读取文件
StreamReader sr = new StreamReader(path, enCoding);
string s = "";
while ((s = sr.ReadLine()) != null)
{
sb.AppendLine(s);
}
if(sr != null)
sr.Close();

return sb.ToString();
}
/// <summary>
/// 获取文件编码格式
/// </summary>
/// <param name="path">文件路径</param>
/// <param name="defaultEncoding">默认编码</param>
/// <returns></returns>
public static string getFileEncoding(string path, string defaultEncoding) {
string ed = defaultEncoding;
if (File.Exists(path)) {
FileStream fs = new FileStream(path, FileMode.Open);
ed = GetEncoding(fs, defaultEncoding);
if (fs != null)
fs.Close();
}
return ed;
}
/// <summary>
/// 取得一个文本文件流的编码方式。
/// </summary>
/// <param name="stream">文本文件流。</param>
/// <param name="defaultEncoding">默认编码方式。当该方法无法从文件的头部取得有效的前导符时，将返回该编码方式。</param>
/// <returns></returns>
public static string GetEncoding(FileStream stream, string defaultEncoding)
{
string targetEncoding = defaultEncoding;
if (stream != null && stream.Length >= 2)
{
//保存文件流的前4个字节
byte byte1 = 0;
byte byte2 = 0;
byte byte3 = 0;
byte byte4 = 0;
//保存当前Seek位置
long origPos = stream.Seek(0, SeekOrigin.Begin);
stream.Seek(0, SeekOrigin.Begin);

int nByte = stream.ReadByte();
byte1 = Convert.ToByte(nByte);
byte2 = Convert.ToByte(stream.ReadByte());
if (stream.Length >= 3)
{
byte3 = Convert.ToByte(stream.ReadByte());
}
if (stream.Length >= 4)
{
byte4 = Convert.ToByte(stream.ReadByte());
}
//根据文件流的前4个字节判断Encoding
//Unicode {0xFF, 0xFE};
//BE-Unicode {0xFE, 0xFF};
//UTF8 = {0xEF, 0xBB, 0xBF};
if (byte1 == 0xFE && byte2 == 0xFF)//UnicodeBe
{
targetEncoding = Encoding.BigEndianUnicode.BodyName;
}
if (byte1 == 0xFF && byte2 == 0xFE && byte3 != 0xFF)//Unicode
{
targetEncoding = Encoding.Unicode.BodyName;
}
if (byte1 == 0xEF && byte2 == 0xBB && byte3 == 0xBF)//UTF8
{
targetEncoding = Encoding.UTF8.BodyName;
}
//恢复Seek位置
stream.Seek(origPos, SeekOrigin.Begin);
}
return targetEncoding;
}

}

class httpClient
{
/// <summary>
/// 获取基础WebRequest
/// </summary>
/// <param name="url">请求地址</param>
/// <param name="lStartPos">请求的开始位置</param>
/// <returns></returns>
public static HttpWebRequest getWebRequest(string url, int lStartPos)
{
HttpWebRequest request = null;
try
{
request = (System.Net.HttpWebRequest)HttpWebRequest.Create(url);
request.AddRange(lStartPos); //设置Range值
}
catch (Exception ex)
{
// Program.print(ex.Message);
}

return request;
}
}
}